Multicomponent superabsorbent gel particles

ABSTRACT

Multicomponent superabsorbent gel particles are disclosed. The multicomponent particles comprise at least one acidic water-absorbing resin and at least one basic water-absorbing resin. Each particle contains at least one microdomain of the acidic resin in contact with, or in close proximity to, at least one microdomain of the basic resin.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.08/974,125, filed Nov. 19, 1997, now U.S. Pat. No. 6,072,101.

FIELD OF THE INVENTION

The present invention relates to multi-component superabsorbent gelparticles containing at least one acidic water-absorbing resin and atleast one basic water-absorbing resin. Each superabsorbent gel particlehas at least one microdomain of the acidic resin in contact with, or inclose proximity to, at least one microdomain of the basic resin.

BACKGROUND OF THE INVENTION

Water-absorbing resins are widely used in sanitary goods, hygienicgoods, wiping cloths, water-retaining agents, dehydrating agents, sludgecoagulants, disposable towels and bath mats, disposable door mats,thickening agents, disposable litter mats for pets,condensation-preventing agents, and release control agents for variouschemicals. Water-absorbing resins are available in a variety of chemicalforms, including substituted and unsubstituted natural and syntheticpolymers, such as hydrolysis products of starch acrylonitrile graftpolymers, carboxymethylcellulose, crosslinked polyacrylates, sulfonatedpolystyrenes, hydrolyzed polyacrylamides, polyvinyl alcohols,polyethylene oxides, polyvinylpyrrolidones, and polyacrylonitriles.

Such water-absorbing resins are termed "superabsorbent polymers," orSAPs, and typically are lightly crosslinked hydrophilic polymers. SAPsare generally discussed in Goldman et al. U.S. Pat. Nos. 5,669,894 and5,559,335, the disclosures of which are incorporated herein byreference. SAPs can differ in their chemical identity, but all SAPs arecapable of absorbing and retaining amounts of aqueous fluids equivalentto many times their own weight, even under moderate pressure. Forexample, SAPs can absorb one hundred times their own weight, or more, ofdistilled water. The ability to absorb aqueous fluids under a confiningpressure is an important requirement for an SAP used in a hygienicarticle, such as a diaper.

As used here and hereafter, the term "SAP particles" refers tosuperabsorbent polymer particles in the dry state, i.e., particlescontaining from no water up to an amount of water less than the weightof the particles. The terms "SAP gel" or "SAP hydrogel" refer to asuperabsorbent polymer in the hydrated state, i.e., particles that haveabsorbed at least their weight in water, and typically several timestheir weight in water.

The dramatic swelling and absorbent properties of SAPs are attributed to(a) electrostatic repulsion between the charges along the polymerchains, and (b) osmotic pressure of the counter ions. It is known,however, that these absorption properties are drastically reduced insolutions containing electrolytes, such as saline, urine, and blood. Thepolymers function much less effectively in the presence of suchphysiologic fluids.

The decreased absorbency of electrolyte-containing liquids isillustrated by the absorption properties of a typical, commerciallyavailable SAP, i.e., sodium polyacrylate, in deionized water and in 0.9%by weight sodium chloride (NaCl) solution. The sodium polyacrylate canabsorb 146.2 grams (g) of deionized water per gram of SAP (g/g) at 0psi, 103.8 g of deionized water per gram of polymer at 0.28 psi, and34.3 g of deionized water per gram of polymer of 0.7 psi. In contrast,the same sodium polyacrylate is capable of absorbing only 43.5 g, 29.7g, and 24.8 g of 0.9% aqueous NaCl at 0 psi, 0.28 psi, and 0.7 psi,respectively. The absorption capacity of SAPs for body fluids, such asurine or menses, therefore, is dramatically lower than for deionizedwater because such fluids contain electrolytes. This dramatic decreasein absorption is termed "salt poisoning."

The salt poisoning effect has been explained as follows.Water-absorption and water-retention characteristics of SAPs areattributed to the presence of ionizable functional groups in the polymerstructure. The ionizable groups typically are carboxyl groups, a highproportion of which are in the salt form when the polymer is dry, andwhich undergo dissociation and salvation upon contact with water. In thedissociated state, the polymer chain contains a plurality of functionalgroups having the same electric charge and, thus, repel one another.This electronic repulsion leads to expansion of the polymer structure,which, in turn, permits further absorption of water molecules. Polymerexpansion, however, is limited by the crosslinks in the polymerstructure, which are present in a sufficient number to preventsolubilization of the polymer.

It is theorized that the presence of a significant concentration ofelectrolytes interferes with dissociation of the ionizable functionalgroups, and leads to the "salt poisoning" effect. Dissolved ions, suchas sodium and chloride ions, therefore, have two effects on SAP gels.The ions screen the polymer charges and the ions eliminate the osmoticimbalance due to the presence of counter ions inside and outside of thegel. The dissolved ions, therefore, effectively convert an ionic gelinto a nonionic gel, and swelling properties are lost.

The most commonly used SAP for absorbing electrolyte-containing liquids,such as urine, is neutralized polyacrylic acid, i.e., containing atleast 50%, and up to 100%, neutralized carboxyl groups. Neutralizedpolyacrylic acid, however, is susceptible to salt poisoning. Therefore,to provide an SAP that is less susceptible to salt poisoning, either anSAP different from neutralized polyacrylic acid must be developed, orthe neutralized polyacrylic acid must be modified or treated to at leastpartially overcome the salt poisoning effect.

The removal of ions from electrolyte-containing solutions is oftenaccomplished using ion exchange resins. In this process, deionization isperformed by contacting an electrolyte-containing solution with twodifferent types of ion exchange resins, i.e., an anion exchange resinand a cation exchange resin. The most common deionization procedure usesan acid resin (i.e., cation exchange) and a base resin (i.e., anionexchange). The two-step reaction for deionization is illustrated withrespect to the desalinization of water as follows:

NaCl+R--SO₃ H→R--SO₃ Na+HCl

HCl+R--N(CH₃)₃ OH→R--N(CH₃)₃ Cl+H₂ O.

The acid resin (R--SO₃ H) removes the sodium ion; and the base resin(R--N(CH₃)₃ QH) removes the chloride ions. This ion exchange reaction,therefore, produces water as sodium chloride is adsorbed onto theresins. The resins used in ion exchange do not absorb significantamounts of water.

The most efficient ion exchange occurs when strong acid and strong baseresins are employed. However, weak acid and weak base resins also can beused to deionize saline solutions. The efficiency of variouscombinations of acid and base exchange resins are as follows:

Strong acid--strong base (most efficient)

Weak acid--strong base

Strong acid--weak base

Weak acid--weak base (least efficient).

The weak acid/weak base resin combination requires that a "mixed bed"configuration be used to obtain deionization. The strong acid/strongbase resin combination does not necessarily require a mixed bedconfiguration to deionize water. Deionization also can be achieved bysequentially passing the electrolyte-containing solution through astrong acid resin and strong base resin.

A "mixed bed" configuration of the prior art is simply a physicalmixture of an acid ion exchange resin and a base ion exchange resin inan ion exchange column, as disclosed in Battaerd U.S. Pat. No.3,716,481. Other patents directed to ion exchange resins having one ionexchange resin imbedded in a second ion exchange resin are Hatch U.S.Pat. No. 3,957,698, Wade et al. U.S. Pat. No. 4,139,499, Eppinger et al.U.S. Pat. No. 4,229,545, and Pilkington U.S. Pat. No. 4,378,439.Composite ion exchange resins also are disclosed in Hatch U.S. Pat. Nos.3,041,092 and 3,332,890, and Weiss U.S. Pat. No. 3,645,922.

The above patents are directed to nonswelling resins that can be used toremove ions from aqueous fluids, and thereby provide purified water. Ionexchange resins used for water purification must not absorb significantamounts of water because resin swelling resulting from absorption canlead to bursting of the ion exchange containment column.

Ion exchange resins or fibers also have been disclosed for use inabsorbent personal care devices (e.g., diapers) to control the pH offluids that reach the skin, as set forth in Berg et al., U.S. Pat. No.4,685,909. The ion exchange resin is used in this application to reducediaper rash, but the ion exchange resin is not significantly waterabsorbent and, therefore, does not improve the absorption and retentionproperties of the diaper.

Ion exchange resins having a composite particle containing acid and baseion exchange particles embedded together in a matrix resin, or havingacid and base ion exchange particles adjacent to one another in aparticle that is free of a matrix resin are disclosed in B. A. Bolto etal., J. Polymer Sci. :Symposium No. 55, John Wiley and Sons, Inc.(1976), pages 87-94. The Bolto et al. publication is directed toimproving the reaction rates of ion exchange resins for waterpurification and does not utilize resins that absorb substantial amountsof water.

Other investigators have attempted to counteract the salt poisoningeffect and thereby improve the performance of SAPs with respect toabsorbing electrolyte-containing liquids, such as menses and urine. Forexample, Tanaka et al. U.S. Pat. No. 5,274,018 discloses an SAPcomposition comprising a swellable hydrophilic polymer, such aspolyacrylic acid, and an amount of an ionizable surfactant sufficient toform at least a monolayer of surfactant on the polymer. In anotherembodiment, a cationic gel, such as a gel containing quaternizedammonium groups and in the hydroxide (i.e., OH) form, is admixed with ananionic gel (i.e., a polyacrylic acid) to remove electrolytes from thesolution by ion exchange. Quaternized ammonium groups in the hydroxideform are very difficult and time-consuming to manufacture, therebylimiting the practical use of such cationic gels.

Wong U.S. Pat. No. 4,818,598 discloses the addition of a fibrous anionexchange material, such as DEAE (diethylaminoethyl) cellulose, to ahydrogel, such as a polyacrylate, to improve absorption properties. Theion exchange resin "pretreats" the saline solution (e.g., urine) as thesolution flows through an absorbent structure (e.g., a diaper). Thispretreatment removes a portion of the salt from the saline. Theconventional SAP present in the absorbent structure then absorbs thetreated saline more efficiently than untreated saline. The ion exchangeresin, per se, does not absorb the saline solution, but merely helpsovercome the "salt poisoning" effect.

WO 96/17681 discloses admixing discrete anionic SAP particles, such aspolyacrylic acid, with discrete polysaccharide-based cationic SAPparticles to overcome the salt poisoning effect. Similarly, WO 96/15163discloses combining a cationic SAP having at least 20% of the functionalgroups in a basic (i.e., OH) form with a cationic exchange resin, i.e.,a nonswelling ion exchange resin, having at least 50% of the functionalgroups in the acid form. WO 96/1518 discloses an absorbent materialcomprising an anionic SAP, e.g., a polyacrylic acid and an anionexchange resin, i.e., a nonswelling ion exchange resin.

These references disclose combinations that attempt to overcome the saltpoisoning effect. However, the references merely teach the admixture oftwo types of particles, and do not suggest a single particle containingat least one microdomain of an acidic resin in contact, or in closeproximity, with at least one microdomain of a basic resin. It would bedesirable to provide discrete SAP particles that exhibit exceptionalwater absorption and retention properties, especially with respect toelectrolyte-containing liquids, and thereby overcome the salt poisoningeffect.

In addition, it would be desirable to provide discrete SAP particlesthat have an ability to absorb liquids quickly, demonstrate good fluidpermeability and conductivity into and through the SAP particle, andhave a high gel strength such that the hydrogel formed from the SAPparticles does not deform or flow under an applied stress or pressure.

SUMMARY OF THE INVENTION

The present invention is directed to multicomponent SAPs comprising atleast one acidic water-absorbing resin, such as a polyacrylic acid, andat least one basic water-absorbing resin, such as poly(vinylamine), apolyethyleneimine, or a poly(dialkylaminoalkyl acrylamide) or apoly(dialkylaminoalkyl methacrylamide), hereafter collectively referredto as poly(dialkylaminoalkyl (meth)acrylamides).

More particularly, the present invention is directed to multicomponentSAP particles containing at least one discrete microdomain of at leastone acidic water-absorbing resin in contact with, or in close proximityto, at least one microdomain of at least one basic water-absorbingresin. The multicomponent SAP particles can contain a plurality ofmicrodomains of the acidic water-absorbing resin and/or the basicwater-absorbing resin dispersed throughout the particle. The acidicresin can be a strong or a weak acidic resin. Similarly, the basic resincan be a strong or a weak basic resin. A preferred SAP contains one ormore microdomains of at least one weak acidic resin and one or moremicrodomains of at least one weak basic resin. The propertiesdemonstrated by such preferred multicomponent SAP particles areunexpected because, in ion exchange applications, the combination of aweak acid and a weak base is the least effective of any combination of astrong or weak acid ion exchange resin with a strong or weak basic ionexchange resin.

Accordingly, one aspect of the present invention is to provide SAPparticles that have a high absorption rate, have good permeability andgel strength, overcome the salt poisoning effect, and demonstrate animproved ability to absorb and retain electrolyte-containing liquids,such as saline, blood, urine, and menses. The present SAP particlescontain discrete microdomains of acidic and basic resin, and duringhydration, the particles resist coalescence but remain fluid permeable.

Another aspect of the present invention is to provide an SAP havingimproved absorption and retention properties compared to a conventionalSAP, such as sodium polyacrylate. The present multicomponent SAPparticles are produced by any method that positions a microdomain of anacidic water-absorbing resin in contact with, or in close proximity to,a microdomain of a basic water-absorbing resin to provide a discreteparticle. In one embodiment, the SAP particles are produced bycoextruding an acidic water-absorbing hydrogel and a basicwater-absorbing hydrogel to provide multicomponent SAP particles havinga plurality of discrete microdomains of an acidic resin and a basicresin dispersed throughout the particle. Such SAP particles demonstrateimproved absorption and retention properties, and permeability throughand between particles compared to SAP compositions comprising a simpleadmixture of acidic resin particles and basic resin particles.

In another embodiment, the present multicomponent SAP particles can beprepared by admixing dry particles of a basic resin with a hydrogel ofan acidic resin, then extruding the resulting mixture to formmulticomponent SAP particles having microdomains of a basic resindispersed throughout a continuous phase of an acidic resin.Alternatively, dry acidic resin particles can be admixed with a basicresin hydrogel, followed by extruding the resulting mixture to formmulticomponent SAP particles having microdomains of an acidic resindispersed in a continuous phase of a basic resin.

In addition, a multicomponent SAP particle containing microdomains of anacidic resin and a basic resin dispersed in a continuous phase of amatrix resin can be prepared by adding dry particles of the acidic resinand dry particles of the basic resin to a hydrogel of the matrixhydrogel, then extruding. Other forms of the present multicomponent SAPparticles, such as agglomerated particles, interpenetrating polymernetwork forms, laminar forms, and concentric sphere forms, alsodemonstrate improved fluid absorption and retention properties.

In accordance with yet another important aspect of the presentinvention, the acidic and basic resins are lightly crosslinked, such aswith a suitable polyfunctional vinyl polymer. In preferred embodiments,the acidic resin, the basic resin, and/or the entire multicomponent SAPparticle are surface treated or annealed to further improve waterabsorption and retention properties, especially under a load.

Yet another important feature of the present invention is to provide anSAP particle containing at least one microdomain of a weak acidicwater-absorbing resin in contact with at least one microdomain of a weakbasic water-absorbing resin.

An example of a weak acid resin is polyacrylic acid having 0% to 25%neutralized carboxylic acid groups (i.e., DN=0 to DN=25). Examples ofweak basic water-absorbing resins are a poly(vinylamine), apolyethylenimine, and a poly(dialkylaminoalkyl (meth)acrylamide)prepared from a monomer either having the general structure formula (I)##STR1## or the ester analog of (I) having the general structure formula(II) ##STR2## wherein R₁ and R₂, independently, are selected from thegroup consisting of hydrogen and methyl, Y is a divalent straight chainor branched organic radical having 1 to 8 carbon atoms, and R₃ and R₄,independently, are alkyl radicals having 1 to 4 carbon atoms. Examplesof a strong basic water-absorbing resin are poly(vinylguanidine) andpoly(allylguanidine).

These and other aspects and advantages of the present invention willbecome apparent from the following detailed description of the preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a water-absorbing particle containingmicrodomains of a first resin dispersed in a continuous phase of asecond resin;

FIG. 2 is a schematic diagram of a water-absorbing particle containingmicrodomains of a first resin and microdomains of a second resindispersed throughout the particle;

FIGS. 3A and 3B are schematic diagrams of a water-absorbing particlehaving a core microdomain of a first resin surrounded by a layer of asecond resin;

FIGS. 4A-D are schematic diagrams of water-absorbing particles having amicrodomain of a first resin in contact with a microdomain of a secondresin;

FIGS. 5A and 5B are schematic diagrams of a water-absorbing particlehaving an interpenetrating network of a first resin and a second resin;

FIG. 6 contains plots of absorbance (in grams of synthetic urine pergram of multicomponent SAP particles) vs. annealing temperature for aone-hour annealing step;

FIG. 7 contains a plot of absorbance (in grams of synthetic urine pergram of multicomponent SAP particles) vs. time for an annealing stepperformed at 125° C.;

FIGS. 8 and 9 contain plots of PUP at 0.7 psi (in g/g) vs. time (hrs)for present multicomponent SAP particles and prior art SAPs; and

FIGS. 10 and 11 contain plots for initial Performance Under Pressure(PUP) capacity vs. t^(1/2) for present multicomponent SAP particles andprior art SAPs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to multicomponent SAP particlescontaining at least one microdomain of an acidic water-absorbing resinin close proximity to, and preferably in contact with, at least onemicrodomain of a basic water-absorbing resin. Each particle contains oneor more microdomains of an acidic resin and one or more microdomains ofa basic resin. The microdomains can be distributed nonhomogeneously orhomogeneously throughout each particle.

Each multicomponent SAP particle of the present invention contains atleast one acidic water-absorbing resin and at least one basicwater-absorbing resin. In one embodiment, the SAP particles consistessentially of acidic resins and basic resins, and contain microdomainsof the acidic and/or basic resins. In another embodiment, microdomainsof the acidic and basic resins are dispersed in an absorbent matrixresin.

The multicomponent SAP particles of the present invention are notlimited to a particular structure or shape. However, it is importantthat substantially each SAP particle contain at least one microdomain ofan acidic water-absorbing resin and at least one microdomain of a basicwater-absorbing resin in close proximity to one another. Improved waterabsorption and retention, and improved fluid permeability through andbetween SAP particles, are observed as long as the acidic resinmicrodomain and the basic resin microdomain are in close proximitywithin the particle. In a preferred embodiment, the microdomains ofacidic and basic resin are in contact.

In some embodiments, an idealized multicomponent SAP particle of thepresent invention is analogous to a liquid emulsion wherein smalldroplets of a first liquid, i.e., the dispersed phase, are dispersed ina second liquid, i.e., the continuous phase. The first and secondliquids are immiscible, and the first liquid, therefore, ishomogeneously dispersed in the second liquid. The first liquid can bewater or oil based, and conversely, the second liquid is oil or waterbased, respectively.

Therefore, in one embodiment, the multicomponent SAP particles of thepresent invention can be envisioned as one or more microdomains of anacidic resin dispersed in a continuous phase of a basic resin, or as oneor more microdomains of a basic resin dispersed in a continuous acidresin.

These idealized multicomponent SAP particles are illustrated in FIG. 1showing an SAP particle 10 having discrete microdomains 14 of adispersed resin in a continuous phase of a second resin 12. Ifmicrodomains 14 comprise an acidic resin, then continuous phase 12comprises a basic resin. Conversely, if microdomains 14 comprise a basicresin, then continuous phase 12 is an acidic resin.

In another embodiment, the SAP particles are envisioned as microdomainsof an acidic resin and microdomains of a basic resin dispersedthrough-out each particle, without a continuous phase. This embodimentis illustrated in FIG. 2, showing an idealized multicomponent SAPparticle 20 having a plurality of microdomains of an acidic resin 22 anda plurality of microdomains of a basic resin 24 dispersed throughoutparticle 20.

In yet another embodiment, microdomains of the acidic and basic resinsare dispersed throughout a continuous phase comprising a matrix resin.This embodiment also is illustrated in FIG. 1 wherein multicomponent SAPparticle 10 contains one or more microdomains 14, each an acidic resinor a basic resin, dispersed in a continuous phase 12 of a matrix resin.

It should be understood that the microdomains within each particle canbe of regular or irregular shape, and that the microdomains can bedispersed homogeneously or nonhomogeneously throughout each particle.Accordingly, another embodiment of the SAP particles is illustrated inFIG. 3A, showing an idealized multicomponent particle having a core 32of an acidic water-absorbing resin surrounded by a shell 34 of a basicwater-absorbing resin. Conversely, core 32 can comprise a basic resin,and shell 34 can comprise an acidic resin.

FIG. 3B illustrates a similar embodiment having a core and concentricshells that alternate between shells of acidic resin and basic resin. Inone embodiment, core 42 and shell 46 comprise an acidic water-absorbingresin, and shell 44 comprises a basic water-absorbing resin. Otherembodiments include: core 42 and shell 46 comprising a basic resin andshell 44 comprising an acidic resin, or core 42 comprising a matrixresin and shells 44 and 46 comprising an acidic resin and a basic resinin alternating shells. Other configurations are apparent to personsskilled in the art, such as increasing the number of shells around thecore.

FIGS. 4A and 4B illustrate embodiments of the present SAP particleswherein one microdomain of an acidic water-absorbing resin (i.e., 52 or62) is in contact with one microdomain of a basic water-absorbing resin(i.e., 54 or 64) to provide a multicomponent SAP particle (i.e., 50 or60). In these embodiments, the microdomains are dispersednonhomogeneously throughout the particle. The embodiments illustrated inFIG. 4 extend to SAP particles having more than one microdomain of eachof the acidic resin and the basic resin, as illustrated in FIGS. 4C and4D, wherein multicomponent SAP particles 70 and 80 contain alternatingzones of acidic water-absorbing resin (e.g., 72 or 82) and basicwater-absorbing resin (e.g., 74 or 84). Particles 70 and 80 also cancontain one or more layers 72, 74, 82, or 84 comprising a matrix resin.

In another embodiment, the multicomponent SAP particle comprises aninterpenetrating polymer network (IPN), as illustrated in FIG. 5. An IPNis a material containing two polymers, each in network form. In an IPN,two polymers are synthesized and/or crosslinked in the presence of oneanother, and polymerization can be sequential or simultaneous.Preparation of a sequential IPN begins with the synthesis of a firstcrosslinked polymer. Then, monomers comprising a second polymer, acrosslinker, and initiator are swollen into the first polymer, andpolymerized and crosslinked in situ. For example, a crosslinkedpoly(acrylic acid) network can be infused with solution containing apoly(vinylamine) and a crosslinker.

Simultaneous IPNs are prepared using a solution containing monomers ofboth polymers and their respective crosslinkers, which then arepolymerized simultaneously by noninterfering modes, such as stepwise orchain polymerizations. A third method of synthesizing IPNs utilizes twolattices of linear polymers, mixing and coagulating the lattices, andcrosslinking the two components simultaneously. Persons skilled in theart are aware of other ways that an IPN can be prepared, each yielding aparticular topology.

In most IPNs, the polymer phases separate to form distinct zones of thefirst polymer and distinct zones of the second polymer. In the remainingIPNs, the first and second polymers remain "soluble" in one another.Both forms of IPN have microdomains, and are multicomponent SAPs of thepresent invention.

FIGS. 5A and 5B illustrate IPN systems. FIG. 5A illustrates an IPN madeby sequentially synthesizing the first and second polymers. FIG. 5Billustrates an IPN made by simultaneously polymerizing the first andsecond polymers. In FIGS. 5A and 5B, the solid lines represent the firstpolymer (e.g., the acidic polymer) and the lightly dotted linesrepresent the second polymer (e.g., the basic polymer). The heavy dotsrepresent crosslinking sites.

In another embodiment, the multicomponent SAP particles are agglomeratedparticles prepared from fine particles of an acidic water-absorbingresin and fine particles of a basic water-absorbing resin. Typically, afine resin particle has a diameter of less than about 200 microns (μ),such as about 0.01 to about 180 μ. The agglomerated multicomponent SAPparticles are similar in structure to the particle depicted in FIG. 2.With respect to the agglomerated SAP particles, it is important that theparticles have sufficient dry agglomeration (i.e., in the dry state) andwet agglomeration (i.e., in the hydrogel state) to retain singleparticle properties, i.e., the particles do not disintegrate into theirconstituent fine particles of acidic resin and basic resin.

In particular, the agglomerated particles have sufficient dryagglomeration to withstand fracturing. The dry agglomerated particlestypically have an elastic character and, therefore, are not friable. Theagglomerated particles also have sufficient wet strength to exhibit aproperty termed "wet agglomeration." Wet agglomeration is defined as theability of an agglomerated multicomponent SAP particle to retain itssingle particle nature upon hydration, i.e., a lack of deagglomerationupon hydration. Wet agglomeration is determined by positioning fiftyagglomerated SAP particles on a watch glass and hydrating the particleswith 20 times their weight of a 1% (by weight) sodium chloride solution(i.e., 1% saline). The particles are spaced sufficiently apart such thatthey do not contact one another after absorbing the saline and swelling.The SAP particles are allowed to absorb the saline solution for onehour, then the number of SAP particles is recounted under a microscope.The multicomponent SAP particles pass the wet agglomeration test if nomore than about 53 hydrated particles are counted.

The multicomponent SAP particles of the present invention thereforecomprise an acidic resin and a basic resin in a weight ratio of about90:10 to about 10:90, and preferably about 20:80 to about 80:20. Toachieve the full advantage of the present invention, the weight ratio ofacidic resin to basic resin in a multicomponent SAP particle is about30:70 to about 70:30. The acidic and basic resins can be distributedhomogeneously or nonhomogeneously throughout the SAP particle.

The present multicomponent SAP particles contain at least about 50%, andpreferably at least about 70%, by weight of acidic resin plus basicresin. To achieve the full advantage of the present invention, amulticomponent SAP particle contains about 80% to 100% by weight of theacidic resin plus basic resin. Components of the present SAP particles,other than the acidic and basic resin, typically, are matrix resins orother minor optional ingredients.

The multicomponent SAP particles of the present invention can be in anyform, either regular or irregular, such as granules, fibers, beads,powders, flakes, or foams, or any other desired shape, such as a sheetof the multicomponent SAP. In embodiments wherein the multicomponent SAPis prepared using an extrusion step, the shape of the SAP is determinedby the shape of the extrusion die. The shape of the multicomponent SAPparticles also can be determined by other physical operations, such asmilling or by the method of preparing the particles, such asagglomeration.

In one preferred embodiment, the present SAP particles are in the formof a granule or a bead, having a particle size of about 10 to about10,000 microns (μm), and preferably about 100 to about 1,000 μm. Toachieve the full advantage of the present invention, the multicomponentSAP particles have a particle size of about 150 to about 800 μm.

A microdomain is defined as a volume of an acidic resin or a basic resinthat is present in a multicomponent SAP particle. Because eachmulticomponent SAP particle contains at least one microdomain of anacidic resin, and at least one microdomain of a basic resin, amicrodomain has a volume that is less than the volume of themulticomponent SAP particle. A microdomain, therefore, can be as largeas about 90% of the volume of multicomponent SAP particles.

Typically, a microdomain has a diameter of about 750 μm or less, andpreferably about 100 μm or less. To achieve the full advantage of thepresent invention, a microdomain has a diameter of about 20 μm or less.The multicomponent SAP particles also contain microdomains that havesubmicron diameters, e.g., microdomain diameters of less than 1 μm,preferably less than 0.1 um, to about 0.01 μm.

In another preferred embodiment, the multicomponent SAP particles are inthe shape of a fiber, i.e., an elongated, acicular SAP particle. Thefiber can be in the shape of a cylinder, for example, having a minordimension (i.e., diameter) and a major dimension (i.e., length). Thefiber also can be in the form of a long filament that can be woven. Suchfilament-like fibers have a weight of below about 80 decitex, andpreferably below about 70 decitex, per filament, for example, about 2 toabout 60 decitex per filament. Tex is the weight in grams per onekilometer of fiber. One tex equals 10 decitex. For comparison,poly(acrylic acid) is about 4 decitex, and poly(vinylamine) is about 80decitex.

Cylindrical multicomponent SAP fibers have a minor dimension (i.e.,diameter of the fiber) less than about 1 mm, usually less than about 500μm, and preferably less than 250 μm, down to about 50 μm. Thecylindrical SAP fibers can have a relatively short major dimension, forexample, about 1 mm, e.g., in a fibrid, lamella, or flake-shapedarticle, but generally the fiber has a length of about 3 to about 100mm. The filament-like fibers have a ratio of major dimension to minordimension of at least 500 to 1, and preferably at least 1000 to 1, forexample, up to and greater than 10,000 to 1.

Each multicomponent SAP particle contains one or more microdomains of anacidic water-absorbing resin and one or more microdomains of a basicwater-absorbing resin, either in contact or in close proximity to oneanother. As illustrated hereafter, the microdomain structure of thepresent SAP particles provides improved fluid absorption (both in amountof fluid absorbed and retained, and rate of absorption) compared to anSAP comprising a simple mixture of discrete acidic SAP resin particlesand discrete basic SAP resin particles. In accordance with anotherimportant feature of the present invention, the present multicomponentSAP particles also demonstrated improved permeability, both through anindividual particle and between particles. The present SAP particles,therefore, have an improved ability to rapidly absorb a fluid, even in"gush" situations, for example, when used in diapers to absorb urine.

The features of good permeability, absorption and retention properties,especially of electrolyte-containing liquids, demonstrated by thepresent multicomponent SAP particles, is important with respect topractical uses of an SAP. These improved properties are attributed, inpart, to the fact that electrolyte removal from the liquid isfacilitated by contacting a single particle (which, in effect, performsan essentially simultaneous deionization of the liquid), as opposed tothe liquid having to contact individual acidic and basic particles(which, in effect, performs a sequential two-step deionization).

If a blend of acidic resin particles and basic resin particles is used,the particles typically have a small particle size. A small particlesize is required to obtain desirable desalination kinetics, because theelectrolyte is removed in a stepwise manner, with the acidic resinremoving the cation and the basic resin removing the anion. Theelectrolyte-containing fluid, therefore, must contact two particles fordesalination, and this process is facilitated by small particle sizedSAPs. Small particles, however, have the effect of reducing flow of thefluid through and between SAP particles, i.e., permeability is reducedand a longer time is required to absorb the fluid.

In addition, in practical use, such as in diapers, SAPs are used inconjunction with a cellulosic pulp. If a blend of acidic resin particlesand basic resin particles is used as the SAP, the cellulosic pulp cancause a separation between the acidic resin particles and basic resinparticles, which adversely affects desalination. The present multidomaincomposites overcome this problem because the acidic resin and basicresin are present in a single particle. The introduction of cellulosicpulp, therefore, cannot separate the acidic and basic resin and cannotadversely affect desalination by the SAP.

A single multicomponent SAP particle simultaneously desalinates anelectrolyte-containing liquid. Desalination is essentially independentof particle size. Accordingly, the present multicomponent SAP particlescan be of a larger size. These features allow for improved liquidpermeability through and between the SAP particles, and results in amore rapid absorption of the electrolyte-containing liquid.

The following schematic reactions illustrate the reactions which occurto deionize, e.g., desalinate, an aqueous saline solution, and that areperformed essentially simultaneously in a single microcomposite SAPparticle, but are performed step-wise in a simple mixture of acidic andbasic resins:

R--CO₂ H+NaCl→R--CO₂ ⁻ Na⁺ +HCl

(acidic resin)

R--NH₂ +HCl→R--NH₃ ⁺ +Cl⁻

(basic resin).

The present multicomponent SAP particle, can be in a form wherein amicrodomain of an acidic water-absorbing resin is in contact with amicrodomain of a basic water-absorbing resin. In another embodiment, theSAP particles can be in a form wherein at least one microdomain of anacidic water-absorbing resin is dispersed in a continuous phase of abasic water-absorbing resin. Alternatively, the multicomponent SAP canbe in a form wherein at least one microdomain of a basic resin isdispersed in a continuous phase of an acidic resin. In anotherembodiment, at least one microdomain of one or more acidic resin and atleast one microdomain of one or more basic resin comprise the entire SAPparticle, and neither type of resin is considered the dispersed or thecontinuous phase. In yet another embodiment, at least one microdomain ofan acidic resin and at least one microdomain of a basic resin aredispersed in a matrix resin.

An acidic water-absorbing resin present in a multicomponent SAP particlecan be either a strong or a weak acidic water-absorbing resin. Theacidic water-absorbing resin can be a single resin, or a mixture ofresins. The acidic resin can be a homopolymer or a copolymer. Theidentity of the acidic water-absorbing resin is not limited as long asthe resin is capable of swelling and absorbing at least ten times itsweight in water, when in a neutralized form. The acidic resin is presentin its acidic form, i.e., about 75% to 100% of the acidic moieties arepresent in the free acid form. As illustrated hereafter, although thefree acid form of a acidic water-absorbing resin is generally a poorwater absorbent, the combination of an acidic resin and a basic resin ina present multicomponent SAP particle provides excellent waterabsorption and retention properties.

The acidic water-absorbing resin typically is a lightly crosslinkedacrylic-type resin, such as lightly crosslinked polyacrylic acid. Thelightly crosslinked acidic resin typically is prepared by polymerizingan acidic monomer containing an acyl moiety, e.g., acrylic acid, or amoiety capable of providing an acid group, i.e., acrylonitrile, in thepresence of a crosslinker, i.e., a polyfunctional organic compound. Theacidic resin can contain other copolymerizable units, i.e., othermonoethylenically unsaturated comonomers, well known in the art, as longas the polymer is substantially, i.e., at least 10%, and preferably atleast 25%, acidic monomer units. To achieve the full advantage of thepresent invention, the acidic resin contains at least 50%, and morepreferably, at least 75%, and up to 100%, acidic monomer units. Theother copolymerizable units can, for example, help improve thehydrophilicity of the polymer.

Ethylenically unsaturated carboxylic acid and carboxylic acid anhydridemonomers useful in the acidic water-absorbing resin include acrylicacid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid,α-cyanoacrylic acid, β-methylacrylic acid (crotonic acid),α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid,α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid,β-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic acid,glutaconic acid, aconitic acid, maleic acid, furmaric acid,tricarboxyethylene, and maleic anhydride.

Ethylenically unsaturated sulfonic acid monomers include aliphatic oraromatic vinyl sulfonic acids, such as vinylsulfonic acid, allylsulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid,acrylic and methacrylic sulfonic acids, such as sulfoethyl acrylate,sulfoethyl ethacrylate, sulfopropyl acrylate, sulfopropyl methacrylate,2-hydroxy-3-methacryloxypropyl sulfonic acid, and2-acrylamide-2-methylpropane sulfonic acid.

As set forth above, polymerization of acidic monomers, andcopolymerizable monomers, if present, most commonly is performed by freeradical processes in the presence of a polyfunctional organic compound.The acidic resins are crosslinked to a sufficient extent such that thepolymer is water insoluble. Crosslinking renders the acidic resinssubstantially water insoluble, and, in part, serves to determine theabsorption capacity of the resins. For use in absorption applications,an acidic resin is lightly crosslinked, i.e., has a crosslinking densityof less than about 20%, preferably less than about 10%, and mostpreferably about 0.01% to about 7%.

A crosslinking agent most preferably is used in an amount of less thanabout 7 wt %, and typically about 0.1 wt % to about 5 wt %, based on thetotal weight of monomers. Examples of crosslinking polyvinyl monomersinclude, but are not limited to, polyacrylic (or polymethacrylic) acidesters represented by the following formula (III); and bisacrylamides,represented by the following formula (IV). ##STR3## wherein x isethylene, propylene, trimethylene, cyclohexyl, hexamethylene,2-hydroxypropylene, --(CH₂ CH₂ O)_(n) CH₂ CH₂ --, or ##STR4## n and mare each an integer 5 to 40, and k is 1 or 2; ##STR5## wherein 1 is 2 or3.

The compounds of formula (III) are prepared by reacting polyols, such asethylene glycol, propylene glycol, trimethylolpropane, 1,6-hexanediol,glycerin, pentaerythritol, polyethylene glycol, or polypropylene glycol,with acrylic acid or methacrylic acid. The compounds of formula (IV) areobtained by reacting polyalkylene polyamines, such as diethylenetriamineand triethylenetetramine, with acrylic acid.

Specific crosslinking monomers include, but are not limited to,1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,3-butyleneglycol diacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycoldiacrylate, diethylene glycol dimethacrylate, ethoxylated bisphenol Adiacrylate, ethoxylated bisphenol A dimethacrylate, ethylene glycoldimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanedioldimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycoldiacrylate, polyethylene glycol dimethacrylate, triethylene glycoldiacrylate, triethylene glycol dimethacrylate, tripropylene glycoldiacrylate, tetraethylene glycol diacrylate, tetraethylene glycoldimethacrylate, dipentaerythritol pentaacrylate, pentaerythritoltetraacrylate, pentaerythritol triacrylate, trimethylolpropanetriacrylate, trimethylolpropane trimethacrylate,tris(2-hydroxyethyl)isocyanurate triacrylate,tris(2-hydroxyethyl)isocyanurate trimethacrylate, divinyl esters of apolycarboxylic acid, diallyl esters of a polycarboxylic acid, triallylterephthalate, diallyl maleate, diallyl fumarate,hexamethylenebismaleimide, trivinyl trimellitate, divinyl adipate,diallyl succinate, a divinyl ether of ethylene glycol, cyclopentadienediacrylate, or mixtures thereof. Compounds such as divinylbenzene anddivinyl ether also can be used to crosslink the poly(dialkylaminoalkylacrylamides). Especially preferred crosslinking agents areN,N'-methylenebisacrylamide, N,N'-methylenebismethacrylamide, ethyleneglycol dimethacrylate, and trimethylolpropane triacrylate.

The acidic resin, either strongly acidic or weakly acidic, can be anyresin that acts as an SAP in its neutralized form. The acidic resinstypically contain a plurality of carboxylic acid, sulfonic acid,phosphonic acid, phosphoric acid, and/or sulfuric acid moieties.Examples of acidic resins include, but are not limited to, polyacrylicacid, hydrolyzed starch-acrylonitrile graft copolymers, starch-acrylicacid graft copolymers, saponified vinyl acetate-acrylic estercopolymers, hydrolyzed acrylonitrile copolymers, hydrolyzed acrylamidecopolymers, ethylene-maleic anhydride copolymers, isobutylene-maleicanhydride copolymers, poly(vinylsulfonic acid), poly(vinylphosphonicacid), poly(vinylphosphoric acid), poly(vinylsulfuric acid), sulfonatedpolystyrene, poly(aspartic acid), poly(lactic acid), and mixturesthereof. The preferred acidic resins are the polyacrylic acids.

The multicomponent SAPs can contain individual microdomains that: (a)contain a single acidic resin or (b) contain more than one, i.e., amixture, of acidic resins. The multicomponent SAPs also can containmicrodomains wherein, for the acidic component, a portion of the acidicmicrodomains comprise a first acidic resin or acidic resin mixture, andthe remaining portion comprises a second acidic resin or acidic resinmixture.

Analogous to the acidic resin, the basic water-absorbing resin in thepresent SAP particles can be a strong or weak basic water-absorbingresins. The basic water-absorbing resin can be a single resin or amixture of resins. The basic resin can be a homopolymer or a copolymer.The identity of the basic resin is not limited as long as the basicresin is capable of swelling and absorbing at least 10 times its weightin water, when in a charged form. The weak basic resin typically ispresent in its free base, or neutral, form, i.e., about 75% to about100% of the basic moieties, e.g., amino groups, are present in aneutral, uncharged form. The strong basic resins typically are presentin the hydroxide (OH) or bicarbonate (HCO₃) form.

The basic water-absorbing resin typically is a lightly crosslinkedacrylic-type resin, such as a poly(dialkylaminoalkyl(meth)acrylamide).The basic resin also can be a polymer such as a poly(vinylamine), alightly crosslinked polyethylenimine, a poly(allylamine), apoly(allylguanidine), a poly(dimethyldiallylammonium hydroxide), aquaternized polystyrene derivative, such as ##STR6## aguanidine-modified polystyrene, such as ##STR7## a quaternizedpoly((meth)acrylamide) or ester analog, such as ##STR8## wherein Me ismethyl, R₂ is hydrogen or methyl, n is a number 1 to 8, and q is anumber from 10 to about 100,000, or a poly(vinylguanidine), i.e.,poly(VG), a strong basic water-absorbing resin having the generalstructural formula (V) ##STR9## wherein q is a number from 10 to about100,000, and R₅ and R₆, independently, are selected from the groupconsisting of hydrogen, C₁ -C₄ alkyl, C₃ -C₆ cycloalkyl, benzyl, phenyl,alkyl-substituted phenyl, naphthyl, and similar aliphatic and aromaticgroups. The lightly crosslinked basic water-absorbing resin can containother copolymerizable units and is crosslinked using a polyfunctionalorganic compound, as set forth above with respect to the acidicwater-absorbing resin.

A basic water-absorbing resin used in the present SAP particlestypically contains an amino or a guanidino group. Accordingly, awater-soluble basic resin also can be crosslinked in solution bysuspending or dissolving an uncrosslinked basic resin in an aqueous oralcoholic medium, then adding a di- or polyfunctional compound capableof crosslinking the basic resin by reaction with the amino groups of thebasic resin. Such crosslinking agents include, for example,multifunctional aldehydes (e.g., glutaraldehyde), multifunctionalacrylates (e.g., butanediol diacrylate, TMPTA), halohydrins (e.g.,epichlorohydrin), dihalides (e.g., dibromopropane), disulfonate esters(e.g., ZA(O₂)O--(CH₂)_(n) --OS(O)₂ Z, wherein n is 1 to 10, and Z ismethyl or tosyl), multifunctional epoxies (e.g., ethylene glycoldiglycidyl ether), multifunctional esters (e.g., dimethyl adipate),multifunctional acid halides (e.g., oxalyl chloride), multifunctionalcarboxylic acids (e.g., succinic acid), carboxylic acid anhydrides(e.g., succinic anhydride), organic titanates (e.g., TYZOR AA fromDuPont), melamine resins (e.g., CYMEL 301, CYMEL 303, CYMEL 370, andCYMEL 373 from Cytec Industries, Wayne, N.J.), hydroxymethyl ureas(e.g., N,N'-dihydroxymethyl-4,5-dihydroxyethyleneurea), andmultifunctional isocyanates (e.g., toluene diisocyanate or methylenediisocyanate). Crosslinking agents also are disclosed in Pinschmidt, Jr.et al. U.S. Pat. No. 5,085,787, incorporated herein by reference, and inEP 450 923.

Conventionally, the crosslinking agent is water or alcohol soluble, andpossesses sufficient reactivity with the basic resin such thatcrosslinking occurs in a controlled fashion, preferably at a temperatureof about 25° C. to about 150° C. Preferred crosslinking agents areethylene glycol diglycidyl ether (EGDGE), a water-soluble diglycidylether, and a dibromoalkane, an alcohol-soluble compound.

The basic resin, either strongly or weakly basic, therefore, can be anyresin that acts as an SAP in its charged form. The basic resin typicallycontains amino or guanidino moieties. Examples of basic resins include apoly(vinylamine), a polyethylenimine, a poly(vinylguanidine), apoly(allylamine), a poly(allylguanidine), or a poly(dialkylaminoalkyl(meth)acrylamide) prepared by polymerizing and lightly crosslinking amonomer having the structure ##STR10## or its ester analog ##STR11##wherein R₁ and R₂, independently, are selected from the group consistingof hydrogen and methyl, Y is a divalent straight chain or branchedorganic radical having 1 to 8 carbon atoms, and R₃ and R₄,independently, are alkyl radicals having 1 to 4 carbon atoms. Preferredbasic resins include a poly(vinylamine), polyethylenimine,poly(vinylguanadine), poly(dimethylaminoethyl acrylamide) (poly(DAEA)),and poly(dimethylaminopropyl methacrylamide) (poly(DMAPMA)). Analogousto microdomains of an acidic resin, the present multicomponent SAPs cancontain microdomains of a single basic resin, microdomains containing amixture of basic resins, or microdomains of different basic resins.

The present multicomponent SAPs can be prepared by various methods. Itshould be understood that the exact method of preparing a multicomponentSAP is not limited by the following embodiments. Any method thatprovides a particle having at least one microdomain of an acidic resinin contact with or in close proximity to at least one microdomain of abasic resin is suitable.

In one method, dry particles of a basic resin, optionally surfacecrosslinked and/or annealed, are admixed into a rubbery gel of an acidicresin. The resulting mixture is extruded, then dried, and optionallysurface crosslinked and/or annealed, to provide multicomponent SAPparticles having microdomains of a basic resin dispersed in a continuousphase of an acidic resin. Alternatively, particles of an acidic resin,optionally surface crosslinked and/or annealed, can be admixed into arubbery gel of a basic resin, and the resulting mixture is extruded anddried, and optionally surface crosslinked and/or annealed, to providemulticomponent SAP particles having microdomains of an acidic resindispersed in a continuous phase of a basic resin.

In another method, dry particles of an acidic resin can be admixed withdry particles of a basic resin, and the resulting mixture is formed intoa hydrogel, then extruded, to form multicomponent SAP particles.

In yet another method, a rubbery gel of an acidic resin and a rubberygel of a basic resin, each optionally surface crosslinked and/orannealed, are coextruded, and the coextruded product is dried, andoptionally surface crosslinked and/or annealed, to form multicomponentSAP particles containing microdomains of the acidic resin and the basicresin dispersed throughout the particle.

The method of preparing the present multicomponent SAP particles,therefore, is not limited, and does not require an extrusion step.Persons skilled in the art are aware of other methods of preparationwherein the multicomponent SAP contains at least one microdomain of anacidic resin and at least one microdomain of a basic resin in contact orin close proximity with each other. One example is agglomeration of fineparticles of at least one acidic resin and at least one basic resin witheach other, and optionally a matrix resin, to provide a multicomponentSAP particle containing microdomains of an acidic and/or basic resin.The multicomponent SAP particles can be ground to a desired particlesize, or can be prepared by techniques that yield the desired particlesize. Other nonlimiting methods of preparing an SAP particle of thepresent invention are set forth in the examples.

In embodiments wherein an acidic resin and a basic resin are present asmicrodomains within a matrix of a matrix resin, particles of an acidicresin and a basic resin are admixed with a rubbery gel of a matrixresin, and the resulting mixture is extruded, then dried, to formmulticomponent SAP particles having microdomains of an acidic resin anda basic resin dispersed in a continuous phase of a matrix resin.Alternatively, rubbery gels of an acidic resin, basic resin, and matrixresin can be coextruded to provide a multicomponent SAP containingmicrodomains of an acidic resin, a basic resin, and a matrix resindispersed throughout the particle. In this embodiment, the acidic resin,basic resin, and resulting multicomponent SAP, each can be optionallysurface crosslinked and/or annealed.

The matrix resin is any resin that allows fluid transport such that aliquid medium can contact the acidic and basic resin. The matrix resintypically is a hydrophilic resin capable of absorbing water. Nonlimitingexamples of matrix resins include poly(vinyl alcohol),poly(N-vinylformamide), polyethylene oxide, poly(meth)acrylamide,poly(hydroxyethyl acrylate), hydroxyethylcellulose, methylcellulose, andmixtures thereof. The matrix resin also can be a conventionalwater-absorbing resin, for example, a polyacrylic acid neutralizedgreater than 25 mole %, and typically greater than 50 mole %.

In preferred embodiments, the acidic resin, the basic resin, and/or themulticomponent SAP particles are surface treated and/or annealed.Surface treatment and/or annealing results in surface crosslinking ofthe particle. In especially preferred embodiments, the acidic and/orbasic resins comprising the multicomponent SAP particles are surfacetreated and/or annealed, and the entire multicomponent SAP particle issurface treated and/or annealed. It has been found that surface treatingand/or annealing of an acidic resin, a basic resin, and/or amulticomponent SAP particle of the present invention enhances theability of the resin or multicomponent SAP particle to absorb and retainaqueous media under a load.

Surface crosslinking is achieved by contacting an acidic resin, a basicresin, and/or a multicomponent SAP particle with a solution of a surfacecrosslinking agent to wet predominantly only the outer surfaces of theresin or SAP particle. Surface crosslinking and drying of the resin ormulticomponent SAP particle then is performed, preferably by heating atleast the wetted surfaces of the resin or multicomponent SAP particles.

Typically, the resins and/or SAP particles are surface treated with asolution of a surface crosslinking agent. The solution contains about0.01% to about 4%, by weight, surface crosslinking agent, and preferablyabout 0.4% to about 2%, by weight, surface crosslinking agent in asuitable solvent, for example, water or an alcohol. The solution can beapplied as a fine spray onto the surface of freely tumbling resinparticles or multicomponent SAP particles at a ratio of about 1:0.01 toabout 1:0.5 parts by weight resin or SAP particles to solution ofsurface crosslinking agent. The surface crosslinker is present in anamount of 0% to about 5%, by weight of the resin or SAP particle, andpreferably 0% to about 0.5% by weight. To achieve the full advantage ofthe present invention, the surface crosslinker is present in an amountof about 0.001% to about 0.1% by weight.

The crosslinking reaction and drying of the surface-treated resin ormulticomponent SAP particles are achieved by heating the surface-treatedpolymer at a suitable temperature, e.g., about 25° C. to about 150° C.,and preferably about 105° C. to about 120° C. However, any other methodof reacting the crosslinking agent to achieve surface crosslinking ofthe resin or multicomponent SAP particles, and any other method ofdrying the resin or multicomponent SAP particles, such as microwaveenergy, or the such as, can be used.

With respect to the basic resin, or multicomponent SAP particles havinga basic resin present on the exterior surface of the particles, suitablesurface crosslinking agents include di- or polyfunctional moleculescapable of reacting with amino groups and crosslinking a basic resin.Preferably, the surface crosslinking agent is alcohol or water solubleand possesses sufficient reactivity with a basic resin such thatcrosslinking occurs in a controlled fashion at a temperature of about25° C. to about 150° C.

Nonlimiting examples of suitable surface crosslinking agents for basicresins include:

(a) dihalides and disulfonate esters, for example, compounds of theformula

    Y--(CH.sub.2).sub.p --Y,

wherein p is a number from 2 to 12, and Y, independently, is halo(preferably bromo), tosylate, mesylate, or other alkyl or aryl sulfonateesters;

(b) multifunctional aziridines;

(c) multifunctional aldehydes, for example, glutaraldehyde, trioxane,paraformaldehyde, terephthaldehyde, malonaldehyde, and glyoxal, andacetals and bisulfites thereof;

(d) halohydrins, such as epichlorohydrin;

(e) multifunctional epoxy compounds, for example, ethylene glycoldiglycidyl ether, bisphenol A diglycidyl ether, and bisphenol Fdiglycidyl ether,

(f) multifunctional carboxylic acids and esters, acid chlorides, andanhydrides derived therefrom, for example, di- and polycarboxylic acidscontaining 2 to 12 carbon atoms, and the methyl and ethyl esters, acidchlorides, and anhydrides derived therefrom, such as oxalic acid, adipicacid, succinic acid, dodecanoic acid, malonic acid, and glutaric acid,and esters, anhydrides, and acid chlorides derived therefrom;

(g) organic titanates, such as TYZOR AA, available from E.I. DuPont deNemours, Wilmington, DE;

(h) melamine resins, such as the CYMEL resins available from CytecIndustries, Wayne, NJ;

(i) hydroxymethyl ureas, such asN,N'-dihydroxymethyl-4,5-dihydroxyethylene urea;

(j) multifunctional isocyanates, such as toluene diisocyanate,isophorone diisocyanate, methylene diisocyanate, xylene diisocyanate,and hexamethylene diisocyanate; and

(k) other crosslinking agents for basic water-absorbing resins known topersons skilled in the art.

A preferred surface crosslinking agent is a dihaloalkane, ethyleneglycol diglycidyl ether (EGDGE), or a mixture thereof, which crosslink abasic resin at a temperature of about 25° C. to about 150° C. Especiallypreferred surface crosslinking agents are dibromoalkanes containing 3 to10 carbon atoms and EGDGE.

With respect to the acidic water-absorbing resins, or multicomponent SAPparticles having an acidic resin on the exterior surface of theparticles, suitable surface crosslinking agents are capable of reactingwith acid moieties and crosslinking the acidic resin. Preferably, thesurface crosslinking agent is alcohol soluble or water soluble, andpossesses sufficient reactivity with an acidic resin such thatcrosslinking occurs in a controlled fashion, preferably at a temperatureof about 25° C. to about 150° C.

Nonlimiting examples of suitable surface crosslinking agents for acidicresins include:

(a) polyhydroxy compounds, such as glycols and glycerol;

(b) metal salts;

(c) quaternary ammonium compounds;

(d) a multifunctional epoxy compound;

(e) an alkylene carbonate, such as ethylene carbonate or propylenecarbonate;

(f) a polyaziridine, such as 2,2-bishydroxymethyl butanoltris[3-(1-aziridine propionate]);

(g) a haloepoxy, such as epichlorhydrin;

(h) a polyamine, such as ethylenediamine;

(i) a polyisocyanate, such as 2,4-toluene diisocyanate; and

(j) other crosslinking agents for acidic water-absorbing resins known topersons skilled in the art.

In addition to, or in lieu of, surface treating, the acidic resin, thebasic resin, the matrix resin, or the entire SAP particle, or anycombination thereof, can be annealed to improve water absorption andretention properties under a load. It has been found that heating aresin for a sufficient time at a sufficient temperature above the Tg(glass transition temperature) of the resin or microdomains improves theabsorption properties of the resin. FIGS. 6 and 7 contain graphs showingthe effect of annealing time and temperature on the absorptionproperties of a multicomponent SAP particle of the present inventioncomprising 55% by weight poly(vinylamine) and 45% by weight poly(acrylicacid), made by the method set forth hereafter in Example 12.

The graphs in FIGS. 6 and 7 show that heating an SAP particle of thepresent invention for about 20 to about 120 minutes at a temperature ofabout 60° C. to about 150° C. improves absorption properties. Theabsorption properties, i.e., AUL and AUNL, graphed in FIGS. 6 and 7 arediscussed in detail hereafter. Preferably, annealing is performed forabout 30 to about 100 minutes at about 80° C. to about 140° C. Toachieve the full advantage of annealing, the SAP particles are annealedfor about 40 to about 90 minutes at about 100° C. to about 140° C.

In accordance with an important feature of the present invention, astrong acidic resin can be used with either a strong basic resin or aweak basic resin, or a mixture thereof. A weak acidic resin can be usedwith a strong basic resin or a weak basic resin, or a mixture thereof.Preferably, the acidic resin is a weak acidic resin and the basic resinis a weak basic resin. This result is unexpected in view of the ionexchange art wherein a combination of a weak acidic resin and a weakbasic resin does not perform as well as other combinations, e.g., astrong acidic resin and a strong basic resin. In more preferredembodiments, the weak acidic resin, the weak basic resin, and/or themulticomponent SAP particles are surface crosslinked and/or annealed.

As previously discussed, sodium poly(acrylate) conventionally isconsidered the best SAP, and, therefore, is the most widely used SAP incommercial applications. Sodium poly(acrylate) has polyelectrolyticproperties that are responsible for its superior performance inabsorbent applications. These properties include a high charge density,and charge relatively close to the polymer backbone.

However, an acidic resin in the free acid form, or a basic resin in thefree base form, typically do not function as a commercially useful SAPbecause there is no ionic charge on either type of polymer. Apoly(acrylic acid) resin, or a poly(vinylamine) resin, are neutralpolymers, and, accordingly, do not possess the polyelectrolyticproperties necessary to provide SAPs useful commercially in diapers,catamenial devices, and similar absorbent articles. The driving forcefor water absorption and retention, therefore, is lacking. This isillustrated in Tables 1 and 2 showing the relatively poor absorption andretention properties for a neutral poly(DAEA) in absorbing syntheticurine. However, when converted to a salt, an acidic resin, such as apolyacrylic acid, or a basic resin, such as a poly(dialkylaminoalkyl(meth)acrylamide), then behave such as a commercially useful SAP.

It has been found that basic resins, in their free base form, are usefulcomponents in superabsorbent materials further containing an acidicwater-absorbing resin. For example, a superabsorbent material comprisingan admixture of a poly(dialkylaminoalkyl (meth)acrylamide) and an acidicwater-absorbing resin, such as polyacrylic acid, demonstrates good waterabsorption and retention properties. Such an SAP material comprises twouncharged, slightly crosslinked polymers, each of which is capable ofswelling and absorbing aqueous media. When contacted with water or anaqueous electrolyte-containing medium, the two uncharged polymersneutralize each other to form a superabsorbent material. This alsoreduces the electrolyte content of the medium absorbed by polymer,further enhancing the polyelectrolyte effect. Neither polymer in itsuncharged form behaves as an SAP by itself when contacted with water.However, superabsorbent materials, which contain a simple mixture of tworesins, one acidic and one basic, are capable of acting as an absorbentmaterial because the two resins are converted to their polyelectrolyteform. These superabsorbent materials have demonstrated good waterabsorption and retention properties. However, the present multicomponentSAP particles, containing at least one microdomain of an acidic resinand at least one microdomain of a basic resin, exhibit improved waterabsorption and retention, and improved permeability, over simplemixtures of acidic resin particles and basic resin particles.

In the present multicomponent SAP particles, the weak basic resin ispresent in its free base, e.g., amine, form, and the acidic resin ispresent in its free acid form. It is envisioned that a low percentage,i.e., about 25% or less, of the amine and/or acid functionalities can bein their charged form. The low percentage of charged functionalitiesdoes not adversely affect performance of the SAP particles, and canassist in the initial absorption of a liquid. A strong basic resin ispresent in the hydroxide or bicarbonate, i.e., charged, form.

The present multicomponent SAP particles are useful in articles designedto absorb large amounts of liquids, especially electrolyte-containingliquids, such as in diapers and catamenial devices.

The following nonlimiting examples illustrate the preparation of themulticomponent SAP particles of the present invention.

EXAMPLE 1 Preparation of Poly(acrylic acid) 0% Neutralized (Poly(AA)DN=0)

A monomer mixture containing acrylic acid (270 grams), deionized water(810 grams), methylene-bisacrylamide (0.4 grams), sodium persulfate(0.547 grams), and 2-hydroxy-2-methyl-1-phenyl-propan-1-one (0.157grams) was prepared, then sparged with nitrogen for 15 minutes. Themonomer mixture was placed into a shallow glass dish, then the monomermixture was polymerized under 15 mW/cm² of UV light for 25 minutes. Theresulting poly(AA) was a rubbery gel.

The rubbery poly(AA) gel was cut into small pieces, then extrudedthrough a KitchenAid Model K5SS mixer with meat grinder attachment. Theextruded gel was dried in a forced-air oven at 120° C., and finallyground and sized through sieves to obtain the desired particle size.

This procedure provided a lightly crosslinked polyacrylic acid hydrogelwith a degree of neutralization of zero (DN=0).

EXAMPLE 2 Preparation of Poly(dimethylaminoethyl acrylamide) (Poly(DAEA))

A monomer mixture containing 125 grams N-(2-dimethylaminoethyl)acrylamide (DAEA), 300 grams deionized water, 0.6 grammethylenebisacrylamide, and 0.11 grams V-50 initiator (i.e.,2,2'-azobis(2-amidinopropane)hydrochloride initiator available from WakoPure Chemical Industries, Inc., Osaka, Japan) was sparged with argon for15 minutes. Then the resulting reaction mixture was placed in a shallowdish and polymerized under 15 mW/cm² of UV light for 25 minutes. Thepolymerization was exothermic, eventually reaching about 100° C. Theresulting lightly crosslinked poly(DAEA) was a rubbery gel. The rubberypoly(DAEA) gel was crumbled by hand, then dried at 60° C. for 16 hours,and finally ground and sized through sieves to obtain the desiredparticle size.

EXAMPLE 3 Preparation of Poly(dimethylaminopropyl methacrylamide)(Poly(DMAPMA))

A monomer mixture containing DMAPMA monomer (100 grams), deionized water(150 grams), methylene-bisacrylamide (0.76 grams) and V-50 initiator(0.72 grams) was placed in a glass beaker. The monomer mixture waspurged with argon for 25 minutes, covered, and then placed in an oven atabout 60° C. for about 60 hours. The resulting lightly crosslinkedpoly(DMAPMA) was a rubbery gel. The rubbery poly-(DMAPMA) gel wascrumbled by hand, dried at 60° C. for 16 hours, and then ground andsized through sieves to obtain the desired particle size.

EXAMPLE 4 Preparation of a Poly(N-vinylformamide) and a Poly(vinylamine)

A monomer mixture containing N-vinylformamide (250 grams), deionizedwater (250 grams), methylenebisacrylamide (1.09) grams), and V-50initiator (0.42 grams) was placed in a shallow dish, then polymerizedunder an ultraviolet lamp as set forth in Example 1 until the mixturepolymerized into a rubbery gel. The lightly crosslinkedpoly(N-vinylformamide) then was hydrolyzed with a sodium hydroxidesolution to yield a lightly crosslinked poly(vinylamine).

EXAMPLE 5 Preparation of a Strong Acidic Water-Absorbing Resin

A monomer mixture containing acrylic acid (51 grams),2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS, 25.8 grams),deionized water (230 grams), methylenebisacrylamide (0.088 grams),sodium persulfate (0.12 grams), and2-hydroxy-2-methyl-1-phenylpropan-1-one (0.034 grams) was prepared, thenplaced in shallow dish and polymerized under an ultraviolet lamp as setforth in Example 1 until the monomer mixture polymerizes into rubberygel.

The gel was cut into small pieces then extruded through a KitchenAidModel K5SS mixer with a meat grinder attachment. The extruded gel thenwas dried in a forced-air oven at 120° C., ground, and sized throughsieves to obtain the desired particle size.

This resulting lightly crosslinked acidic resin contained 15 molepercent strong acid functionality (--SO₃ H) and 85 mole percent weakacid functionality (--CO₂ H)

EXAMPLE 6 Preparation of a Crosslinked Poly(vinyl alcohol-co-vinylamine)Resin

Poly(vinyl alcohol-co-vinylamine) (50 grams, 6 mol % vinylamine),available from Air Products Inc., Allentown, Pa., was dissolved in 450grams of deionized water in a glass jar to form a viscous solution.Ethylene glycol diglycidyl ether (0.2 grams) was added to the viscoussolution, with stirring. The jar then was covered and placed in a 60° C.oven for 16 hours to yield a rubbery gel of a lightly crosslinkedpoly(vinyl alcohol-co-vinylamine).

EXAMPLE 7 Preparation of a Crosslinked Poly(vinylamine) Resin

To 2 liters of a 3% by weight aqueous poly(vinylamine) solution wasadded 0.18 g of ethyleneglycol diglycidyl ether (EGDGE). The resultingmixture was stirred to dissolve the EGDGE, then the mixture was heatedto about 60° C. and held for one hour to gel. The gel was heated toabout 80° C. and held until about 90% of the water was removed. Theresulting get then was extruded and dried to a constant weight at 80° C.The dried, lightly crosslinked poly(vinylamine) then was cryogenicallymilled to form a granular material.

EXAMPLE 8 Preparation of a Poly(DAEA)/Poly(AA) Multicomponent SAP(Poly(AA) Continuous Phase)

The undried, rubbery poly(AA) hydrogel prepared in Example 1 (133 grams)was cut into pieces and extruded through a KitchenAid Model K5SS mixerwith meat grinder attachment. The gel then was mixed with 50 grams ofthe dry poly(DAEA) particles (<106 microns in size) prepared in Example2. The resulting mixture was extruded three times using the KitchenAidmixer, then dried in a 60° C. forced-air oven for 16 hours and finallyground and sized through sieves to obtain the desired particle size. Theprocess yielded 83 grams of multicomponent SAP particles comprisingpoly(DAEA) microdomains dispersed in a continuous poly(AA) phase, andhaving a weight ratio of poly(DAEA) to poly(AA) of about 60/40.

EXAMPLE 9 Surface Treatment of the Poly(DAEA)/Poly(AA) MulticomponentSAP of Example 8

A surface-treating solution was prepared by admixing 0.15 grams EGDGE,7.88 grams propylene glycol, and 1.97 grams deionized water untilhomogeneous. Ten grams of the poly(DAEA)/poly(AA) multicomponent SAP ofExample 8 were placed in a beaker fitted with a vertical shaft stirrer.The dry multicomponent SAP was stirred at a sufficient speed to fluidizethe SAP in the beaker, then 0.4 grams of the surface-treating solutionwas added to the fluidized SAP dropwise via syringe. Then, stirring wasstopped, and the beaker was placed in a 125C forced-air oven for onehour to yield a poly(DAEA)/poly(AA) multicomponent SAP surface treatedwith 600 ppm of EGDGE.

EXAMPLE 10 Preparation of a Poly(AA)/Poly(DMAPMA) Multicomponent SAP(Poly(DMAPMA) Continuous Phase)

The poly(DMAPMA) hydrogel prepared in Example 3 (70 grams) was cut intopieces and extruded through a KitchenAid Model K5SS mixer with meatgrinder attachment. The gel then was mixed with 32 grams of dry poly(AA)particles (<106 microns in size) prepared in Example 1. The resultingmixture then was extruded three times using the KitchenAid mixer,followed by drying in a 60° C. forced-air oven at 60° C. for 16 hours,and finally grinding and sizing through sieves to obtain the desiredparticle size. The process yielded 60 grams of multicomponent SAPparticles comprising poly(AA) microdomains dispersed in a continuouspoly(DMAPMA) phase, and having a poly(AA) to poly(DMAPMA) weight ratioof about 50/50.

EXAMPLE 11 Surface Treatment of the Poly(AA)/Poly(DMAPMA) MulticomponentSAP of Example 10

A surface-treating solution was prepared by admixing 0.375 grams1,8-dibromooctane and 9.625 grams isopropanol until homogeneous. Tengrams of the poly(AA)/poly(DMAPMA) multicomponent SAP of Example 10 wereplaced in a beaker fitted with a vertical shaft stirrer. The drymulticomponent SAP was stirred at a sufficient speed to fluidize the SAPin the beaker, then 0.4 grams of the surface-treating solution was addedto the fluidized SAP dropwise via syringe. Next, stirring was stopped,and the beaker was placed in a 105° C. forced-air oven for one hour toyield a poly(AA)/poly(DMAPMA) multicomponent SAP surface treated with1,500 ppm of 1,8-dibromooctane.

EXAMPLE 12 Poly(DAEA)/Poly(AA) Multicomponent SAP Prepared by GelCoextrusion

Thirty grams of the poly(DAEA) of Example 2 were extruded through aKitchenAid Model K5SS mixer with meat grinder attachment. Twenty-fourgrams of the poly(AA) hydrogel of Example 1 also were extruded through aKitchenAid Model K5SS mixer with meat grinder attachment. The twoextrudates then were combined via hand mixing, followed by extruding theresulting mixture two times using the meat grinder. The extruded productthen was dried for 16 hours at 60° C., milled and sized to 180-710microns, and finally surface treated with 200 ppm EGDGE (as described inExample 9). The procedure yields multicomponent SAP containingmicrodomains of poly(DAEA) and poly(AA), and having poly(DAEA)/poly(AA)weight ratio of about 60/40.

EXAMPLE 13 Preparation of Poly(vinylguanadine) (Poly(VG))

To 500 ml of an aqueous solution of poly(vinylamine) (1.98% solids, 93%hydrolyzed) was added 38.5 ml of 6M hydrochloric acid and 9.65 g ofcyanamide (H₂ NCN). The resulting solution was heated under reflux for 8hours. The solution next was diluted to a volume of 3 L (liters) with a5% sodium hydroxide solution, then ultrafiltered (M_(w) cut off of100,000) with 15 L of a 5% sodium hydroxide solution, followed by 15 Lof deionized water. The resulting product was concentrated to a 2.6%solids solution, having a pH 11.54. A poly(vinylamine) solution has a pH10.0. The 2.6% solids solution gave a negative silver nitrate test, anda gravimetric analysis of the polymer, after the addition of HCl, gavethe following composition: vinylguanidine 90%, vinylformamide 7%, andvinylamine 3%. Infrared analysis shows a strong absorption at 1651 cm⁻¹,which is not present in poly(vinylamine), and corresponds to a C═Nstretch.

EXAMPLE 14 Preparation of a Crosslinked Poly(VG) Resin

The 2.6% solids solution of Example 13 was further concentrated to 12.5%solids by distillation. To this 12.5% solids solution was added 1 mole %EGDGE, and the resulting solution then was heated in a 60° C. oven for 5hours to form a gel of lightly crosslinked poly(vinylguanidine).

EXAMPLE 15 Preparation of a Coextruded Poly(VG)/Poly(AA) MulticomponentSAP

The crosslinked poly(VG) hydrogel of Example 14 was coextruded with 1mole equivalent of the poly(AA) of Example 1 by the method set forth inExample 12. A portion of the coextruded poly(VG)/poly(AA) multicomponentSAP then was surface crosslinked with 200 ppm EGDGE, by the method setforth in Example 9.

EXAMPLE 16 PEI/Poly(AA) Coextruded Multicomponent SAP Prepared by GelCoextrusion

Aqueous solutions containing 10% and 20% by weight polyethylenimine(PEI, M_(w) of 60,000, available commercially as EPOMIN P-1000, AcetoCorp., Lake Success, N.Y.) were crosslinked with 1.0 and 1.5 mole %EGDGE by the method set forth in Example 6, i.e., heating for 16 hoursat 60° C., to provide rubbery gels. The rubbery PEI gels (37.4 wt. %)were coextruded with the poly(AA) gel of Example 1 (62.6 wt. %) inaccordance with the method set forth in Example 12, and the resultingcoextruded multicomponent SAPs were dried in an oven at 60° C. The driedmulticomponent SAPs were cryogenically milled, and then sized.

In the test results set forth below, the multicomponent SAP particles ofthe present invention were tested for absorption under no load (AUNL)and absorption under load at 0.28 psi and 0.7 psi (AUL (0.28 psi) andAUL (0.7 psi)). Absorption under load (AUL) is a measure of the abilityof an SAP to absorb fluid under an applied pressure. The AUL wasdetermined by the following method, as disclosed in U.S. Pat. No.5,149,335, incorporated herein by reference.

An SAP (0.160 g +/-0.001 g) is carefully scattered onto a 140-micron,water-permeable mesh attached to the base of a hollow plexiglas cylinderwith an internal diameter of 25 mm. The sample is covered with a 100 gcover plate and the cylinder assembly weighed. This gives an appliedpressure of 20 g/cm² (0.28 psi). Alternatively, the sample can becovered with a 250 g cover plate to give an applied pressure of 51 g/cm²(0.7 psi). The screened base of the cylinder is placed in a 100 mm petridish containing 25 milliliters of a test solution (usually 0.9% saline),and the polymer is allowed to absorb for 1 hour (or 3 hours). Byreweighing the cylinder assembly, the AUL (at a given pressure) iscalculated by dividing the weight of liquid absorbed by the dry weightof polymer before liquid contact.

The following tables contain absorption and retention data for themulticomponent SAP particles of the present invention, for individualpolymers present in the multicomponent SAP particles, and for simpleadmixtures of the dry resins present in the multicomponent SAPparticles. The data shows a significant improvement in water absorptionand retention for the present multicomponent SAP particles containingmicrodomains of an acidic and/or basic resin polymers within eachparticle compared to the individual resins and a simple admixture of theindividual resins. The data in Tables 1-6 shows the improved ability ofmulticomponent SAP particles of the present invention to absorb andretain an aqueous 0.9% saline solution.

                                      TABLE 1                                     __________________________________________________________________________                AUL  AUL (0.7  AUL (0.28                                                                           AUL (0.7                                                 (0.28 psi,                                                                         psi, AUNL (1                                                                            psi,  psi, AUNL (3                                 SAP         1 hr.)                                                                             1 hr.)                                                                             hr.) 3 hr.)                                                                              3 hr.)                                                                             hr.)                                    __________________________________________________________________________    Poly(DAEA) alone.sup.1)                                                                    9.6  8.1 23.9 13.5   9.3 24.2                                    Polyacrylic Acid alone.sup.2)                                                             11.9 10.8 14.3 12.0  10.8 14.3                                    SAP-1.sup.3)                                                                              11.0 10.9 45.2 14.8  14.4 48.0                                    SAP-2.sup.4)                                                                              12.5  9.6 26.7 18.9  13.1 30.1                                    SAP-3.sup.5)                                                                              12.4 11.3 37.3 16.5  14.7 42.3                                    SAP-4.sup.6)                                                                              20.1 17.2 28.6 24.7  20.7 34.1                                    SAP-5.sup.7)                                                                              25.3 18.2 35.3 28.1  23   38.7                                    Multicomponent SAP-1.sup.8)                                                      0.sup.9) 23.7 16.3 41.6 26.9  20   41.7                                      200       26.7 24.7 41.2 27.1  25.1 39.9                                      400       27.3 24.1 43.4 27.5  24.5 44.0                                      600       29.2 23.8 41.8 29.5  24.0 41.2                                      800       26.6 24.1 40.9 26.7  24.2 41.7                                    1,000       27.5 24.3 39.9 27.8  24.2 40.7                                    Multicomponent SAP-2.sup.10)                                                     0.sup.9) 26.3 15.4 40   26.9  17.3 39.4                                    400         26.5 20.5 39.3 27    22.4 40.3                                    600         27   18.3 40.2 27.1  20.7 40.6                                    __________________________________________________________________________     .sup.1) particle size-180-710 μm;                                          .sup.2) 0% neutralization, particle size-180-710 μm, surface               crosslinked-600 ppm EGDGE;                                                    .sup.3) mixture of 60% poly(DAEA), particle sizes less than 180 nm, and       40% polyacrylic acid-0% neutralized;                                          .sup.4) mixture of 60% poly(DAEA), particle sizes less than 180 nm, and       40% polyacrylic acid-0% neutralized, crosslinked with 600 ppm EGDGE;          .sup.5) mixture of 60% poly(DAEA), particle size-180-710 μm, and 40%       polyacrylic acid-0% neutralized;                                              .sup.6) mixture of 60% poly(DAEA), particle size-180-710 μm, and 40%       polyacrylic acid-0% neutralized, crosslinked with 600 ppm EGDGE;              .sup.7) mixture of 60% poly(DAEA), particle sizes less than 180 μm, an     40% polyacrylic acid-20% neutralized, particle size 18-710 μm;             .sup.8) multicomponent SAP containing microdomains of poly(DAEA) (<180        μm) as dispersed phase in poly(AA) (DN = 0) continuous phase,              poly(DAEA)/poly(AA) weight ratio-60/40;                                       .sup.9) ppm surface crossiinking with EGDGE; and                              .sup.10) multicomponent SAP containing microdomains of poly(DAEA) (<180       μm) as dispersed phase in poly(AA) (DN = 20) continuous phase,             poly(DAEA)/poly(AA) weight ratio-60/40.                                  

                                      TABLE 2                                     __________________________________________________________________________                AUL  AUL (0.7  AUL (0.28                                                                           AUL (0.7                                                 (0.25 psi,                                                                         psi, AUNL (1                                                                            psi,  psi, AUNL (3                                 SAP         1 hr.)                                                                             1 hr.)                                                                             hr.) 3 hr.)                                                                              3 hr.)                                                                             hr.)                                    __________________________________________________________________________    Poly(DMAPMA).sup.11)                                                                      10.2 8.6  10   11.4  10   18.3                                    Poly(DMAPMA).sup.12)                                                                      9.3  5.2  17.4 11    6.9  17.8                                    Polyacrylic acid.sup.13)                                                                  11.9 10.8 14.3 12.0  10.8 14.3                                    SAP-6.sup.14)                                                                             14.5 10.9 18.8 17.2  14.3 20.9                                    SAP-7.sup.15)                                                                             14   12   38.7 17.9  15.7 43.6                                    SAP-8.sup.16)                                                                             12.5 10.4 24.8 14.5  12.4 24.8                                    Multicomponent SAP-3.sup.17)                                                   0.sup.9)   28.8 15   41.6 31    17.5 41.5                                    100         27.4 24.2 38.8 27.1  23.6 38.8                                    200         27.3 24.2 39.8 25.B  23   39                                      400         26   23   37   25.2  22.5 36.4                                    600         25.1 22.3 37.1 24.7  21.3 36.1                                    Multicomponent SAP-4.sup.18)                                                   0.sup.9)   31.9 11.6 44.2 31.8  15.7 44.9                                    200         27.6 24.3 37.8 27.5  23.4 38.1                                    400         27.5 23.7 37.4 27.2  23.1 38.8                                    Multicomponent SAP-5.sup.19)                                                    0.sup.20) 23.6 12.9 37.9 25    14.4 38.5                                    1500        24.7 16.9 36.4 25.5  18.3 37.5                                    __________________________________________________________________________     .sup.11) Poly(DMAPMA), particle size less than 106 μm;                     .sup.12) Poly(DMAPMA), particle size 106-180 μm;                           .sup.13) Polyacrylic acid, particle size 180-710 μm-0% neutralized,        surface crosslinked with 600 ppm EGDGE;                                       .sup.14) mixture of 60% Poly(DMAPMA), particle size 106-180 μm, and 40     polyacrylic acid-0% neutralized;                                              .sup.15) mixture of 60% Poly(DMAPMA), particle size <106 μm, and 40%       polyacrylic acid-0% neutralized;                                              .sup.16) mixture of 50% Poly(DMAPMA), and 50% polyacrylic acid-0%             neutralized;                                                                  .sup.17) multicomponent SAP containing microdomains of poly(DMAPMA) (<106     μm) as dispersed phase in poly(AA) (DN = 0) continuous phase,              poly(DMAPMA)/poly(AA) weight ratio 60/40;                                     .sup.18) multicomponent SAP containing microdomains of poly(DMAPMA)           (106-180 μm) as dispersed phase in poly(AA) (DN = 0) continuous phase,     poly(DMAPMA)/poly(AA) weight ratio 60/40;                                     .sup.19) multicomponent SAP containing microdomains of poly(AA) (DN = 0%)     (<106 μm) as dispersed phase in poly(DMAPMA) continuous phase,             poly(AA)/poly(DMAPMA) weight ratio 50/50; and                                 .sup.20) ppm surface crosslinking with dibromooctane.                    

                                      TABLE 3                                     __________________________________________________________________________                AUL  AUL (0.7  AUL (0.28                                                                           AUL (0.7                                                 (0.25 psi,                                                                         psi, AUNL (1                                                                            psi,  psi, AUNL (3                                 SAP         1 hr.)                                                                             1 hr.)                                                                             hr.) 3 hr.)                                                                              3 hr.)                                                                             hr.)                                    __________________________________________________________________________    Poly(vinylamine) alone                                                                    14.2 14.4 21.4 15    14.3 23.4                                    SAP-9.sup.21)                                                                             21.2 18.6 28.3 23.8  20.5 36.3                                    Multicomponent SAP-6.sup.22)                                                   0.sup.9)   14.9 12.8 53.8 16.9  15.6 55.4                                    100         37.5 30.1 45.5 37.5  30.1 45.5                                    200         36.2 30.4 48.5 35.9  30.2 47.4                                    400         34.6 30.6 44.9 34.6  30.6 46.2                                    __________________________________________________________________________     .sup.21) mixture of 37% poly(vinylamine) and 63% poly(AA); and                .sup.22) multicomponent SAP containing microdomains of poly(vinylamine)       (<180 μm) as dispersed phase in poly(AA) (DN = 0) continuous phase,        poly(vinylamine)/poly(AA) weight ratio-37/63.                            

                  TABLE 4                                                         ______________________________________                                        Coextruded Multicomponent SAP of Example 12                                   (60/40 weight ratio poly(DAEA)/poly(AA))                                             AUL      AUL           AUL    AUL                                      Surface                                                                              (0.28 psi,                                                                             (0.7 psi,                                                                             AUNL  (0.28 psi,                                                                           (0.7 psi,                                                                           AUNL                               Treatment                                                                            1 hr.)   1 hr.)  (1 hr.)                                                                             3 hr.) 3 hr.)                                                                              (3 hr.)                            ______________________________________                                        0      30.5     13.3    41.1  30.6   16.3  40.2                               200 ppm                                                                              31       27.7    40.2  30.8   27.3  39.9                               EGDGE                                                                         ______________________________________                                    

                                      TABLE 5                                     __________________________________________________________________________                AUL  AUL (0.7  AUL (0.28                                                                           AUL (0.7                                                 (0.25 psi,                                                                         psi, AUNL (1                                                                            psi,  psi, AUNL (3                                 SAP         1 hr.)                                                                             1 hr.)                                                                             hr.) 3 hr.)                                                                              3 hr.)                                                                             hr.)                                    __________________________________________________________________________    Poly(vinylguanidine)                                                                      21   16.1 31.2 22.4  18.0 32.7                                    hydrochloride alone                                                           Multicomponent SAP-7.sup.23)                                                   0.sup.9)     18.8                                                                             12.7 40.6 21.2  15.3 46.8                                    200         22   19.2 33.5 23.5  20.3 37.4                                    __________________________________________________________________________     .sup.23) multicomponent SAP containing microdomains of poly(VG) and           poly(AA), with a poly(VG)/poly(AA) weight ratio-50/50.                   

                                      TABLE 6                                     __________________________________________________________________________    Coextruded Multicomponent SAP of Example 16                                   (37.4/62.6 weight ratio PEI/poly(AA))                                         PEI Gel                                                                           Cross-                                                                             AUL  AUL       AUL  AUL                                              (%  linker                                                                             (0.28 psi,                                                                         (0.7 psi,                                                                          AUNL (0.28 psi,                                                                         (0.7 psi,                                                                         AUNL                                         Solids)                                                                           Level.sup.24)                                                                      1 hr.)                                                                             1 hr.)                                                                             (1 hr.)                                                                            3 hr.)                                                                             3 hr.)                                                                            (3 hr.)                                      __________________________________________________________________________    20  1.0  23   19.5 32   24.3 20.8                                                                              34.9                                         10  1.5  20.1 16.2 28.4 22.4 18.1                                                                              31.9                                         __________________________________________________________________________     .sup.24) mole % EGDGE.                                                   

EXAMPLE 17 Preparation of a Multicomponent SAP Having a Poly(AA) CoreSurrounded by a PEI Shell

Sorbitan monooleate (0.81 g) was dissolved in 200 ml of heptane. Tengrams of crosslinked, unneutralized polyacrylic acid (180-425 μm) wasadded to this solution to act as seed for the core/shell compositeparticles. The resulting mixture was stirred at 700 rpm with a paddlestirrer. Polyethyleneimine (PEI) (27.6 g, 30% in water, M_(w) =750,000)was added to the polyacrylic acid/heptane slurry, followed immediatelyby the addition of 3.6 g of EGDGE. The EGDGE and PEI were allowed tocure for 4.5 hours at room temperature. The resulting SAP particles wereallowed to settle, and the supernatant heptane was decanted. The SAPparticles were rinsed three times with 100 ml of acetone. The SAPparticles were allowed to dry overnight at room temperature, thenfurther dried at 80° C. for 2 hours to yield 23.43 g of themulticomponent SAP particles.

The SAP particles of Example 17 then were tested for an ability toabsorb synthetic urine under no load (AUNL) and under load (AUL) at 0.28psi and 0.7 psi, in accordance with the previously described method. Theresults are summarized below:

    ______________________________________                                                        AUL     AUL         AUL   AUL                                 Surface AUNL    0.28 psi                                                                              0.7 psi                                                                             AUNL  0.28 psi                                                                            0.7 psi                             Treatment                                                                             (1 hr)  (1 hr)  (1 hr)                                                                              (3 hr)                                                                              (3 hr)                                                                              (3 hr)                              ______________________________________                                        None    15.22   12.09   10.38 15.78 13.12 11.74                               ______________________________________                                    

EXAMPLE 18 Preparation of a Multicomponent SAP Having a Poly(AA) CoreSurrounded by a Poly(vinylamine) Shell

Sorbitan monooleate (1.88 g) was dissolved in 500 ml of heptane. Tengrams of crosslinked, unneutralized polyacrylic acid (180-425 μm) wasadded to this solution to act as seed for the core/shell compositeparticles. The resulting mixture was stirred at 700 rpm with a paddlestirrer. Poly(vinylamine) (84 g, 10.67% in water, M_(w) >100,000) wasadded to the polyacrylic acid/heptane slurry, followed immediately bythe addition of 1.5 g of EGDGE. The EGDGE and poly(vinylamine) wereallowed to cure for 6 hours at room temperature. The resulting SAPparticles were allowed to settle, and the supernatant heptane wasdecanted. The SAP particles were rinsed three times with 200 ml ofacetone. The SAP particles were dried at 80° C. for 3 hours to yield17.89 g of the multicomponent SAP particles.

The SAP particles of Example 18 then were tested for an ability toabsorb synthetic urine. The results are summarized below:

    ______________________________________                                                        AUL     AUL         AUL   AUL                                 Surface AUNL    0.28 psi                                                                              0.7 psi                                                                             AUNL  0.28 psi                                                                            0.7 psi                             Treatment                                                                             (1 hr)  (1 hr)  (1 hr)                                                                              (3 hr)                                                                              (3 hr)                                                                              (3 hr)                              ______________________________________                                        None    49.88   39.28   33.20 51.83 41.79 35.23                               ______________________________________                                    

EXAMPLE 19 Preparation of a Multicomponent SAP Containing AgglomeratedPoly(AA) and Poly(vinylamine)

An agglomeration solution containing the following ingredients wasprepared:

0.25 g EGDGE

0.32 g Aluminum sulfate

0.31 g Magnesium sulfate

4.10 g Water

15.0 g Propylene glycol.

Under rapid agitation, 2.1 g of poly(vinylamine) (<180 μm, 5 mole %crosslinked with EGDGE) and 2.38 g of poly(AA) (<180 μm, 0.07 mole %crosslinked with MBA) were fluidized. With continued mixing, 0.84 g ofthe agglomeration solution was added to the fluidized powder blend. Theresulting SAP particles were spread on a glass dish and dried at 125° C.for 2.5 hours.

The ability of the SAP particles to absorb and retain synthetic urinewas determined. The results are summarized below:

    ______________________________________                                                        AUL     AUL         AUL   AUL                                 Surface AUNL    0.28 psi                                                                              0.7 psi                                                                             AUNL  0.28 psi                                                                            0.7 psi                             Treatment                                                                             (1 hr)  (1 hr)  (1 hr)                                                                              (3 hr)                                                                              (3 hr)                                                                              (3 hr)                              ______________________________________                                        None    55.09   40.40   31.22 56.71 41.01 37.80                               ______________________________________                                    

EXAMPLE 20 Preparation of a Multicomponent SAP Comprising anInterpenetrating Polymer Network of Poly(AA) and Poly(vinylamine)

Reticulated poly(sodium acrylate) polymer beads (1.19 g) were acidifiedwith 20 ml of 1M HCl, and allowed to stand for 1.5 hours. The poly(AA)beads then were filtered on a medium glass frit and rinsed with 50 ml ofisopropyl alcohol. Air was drawn through the acidified poly(AA) beadsfor 0.5 hour to remove isopropyl alcohol from the pores of the poly(AA).The poly(AA) foam beads then were added to a premixed solution of 11.0 gof poly(vinylamine) (10.67%, M_(w) >100,000) and 0.24 g of EGDGE. Theresulting mixture coagulated and was allowed to cure for 2 hours at 60°C. The resulting multicomponent SAP particles were spread on a dish anddried at 60° C. overnight to yield 2.8 g of the agglomerated SAPparticles. A portion of the resulting multicomponent SAP particles wasannealed at 125° C. for 1 hour to effect surface crosslinking. Theremaining portion of the particles was not annealed. The ability of theIPN SAP particles of Example 20 were tested for an ability to absorb andretain synthetic urine. The results are summarized below:

    ______________________________________                                                        AUL     AUL         AUL   AUL                                 Surface AUNL    0.28 psi                                                                              0.7 psi                                                                             AUNL  0.28 psi                                                                            0.7 psi                             Treatment                                                                             (1 hr)  (1 hr)  (1 hr)                                                                              (3 hr)                                                                              (3 hr)                                                                              (3 hr)                              ______________________________________                                        None                    22.1              22.4                                Annealing                                                                             32.8    25.2    21.7  34.   22.9  22.8                                for 1 hr                                                                      @ 125° C.                                                              ______________________________________                                    

EXAMPLE 21 Preparation of a Multicomponent SAP Comprising a Layer ofPoly(AA) in Laminar Contact with a Layer of Poly(vinylamine)

To 186 g of 5 wt % poly(AA) (M_(w) of about 1.25×10⁶) in water was added1.18 g of EGDGE, and the viscous solution was mixed thoroughly.Separately, 106 g of poly(vinylamine) (10.67%, M_(w) >100,000) and 2.3 gof EGDGE were quickly mixed and spread on a 9"×13" Teflon-coated metalsheet, then cured at 80° C. for 10 minutes. Next, the poly(AA) solutionwas spread on the poly(vinylamine) gel and allowed to cure and dry at80° C. for 4 hours. The sheets shrunk during drying, and then thelaminate was comminuted. A portion of the resulting multicomponent SAPparticles was neither surface crosslinked nor annealed. A second portionwas annealed at 125° C. for 1 hour. A third portion was surfacecrosslinked with PG/H₂ O at 120° C. in an identical manner as Example19. The SAP particles of Example 21 were tested for an ability to absorband retain synthetic urine. The results are summarized below:

    ______________________________________                                                        AUL     AUL         AUL   AUL                                 Surface AUNL    0.28 psi                                                                              0.7 psi                                                                             AUNL  0.28 psi                                                                            0.7 psi                             Treatment                                                                             (1 hr)  (1 hr)  (1 hr)                                                                              (3 hr)                                                                              (3 hr)                                                                              (3 hr)                              ______________________________________                                        None    32.4    22.4    23.7  35.1  25.1  27                                  Annealed                                                                              25.3    20.1    22.1  29.1  21.7  24.4                                for 1 hr                                                                      @ 125° C.                                                              Cross-  27      20.5    20.8  29.7  22.3  24.7                                linked                                                                        with                                                                          FG/H.sub.2 O                                                                  (80/20)                                                                       ______________________________________                                    

To demonstrate that a multicomponent SAP particle of the presentinvention can contain an acidic resin and/or a basic resin that ispartially neutralized, a series of tests was performed on multicomponentSAP particles containing 45% by weight poly(AA) and 55% by weightpoly(vinylamine). The multicomponent SAP particles were prepared as setforth in Example 12, but the percent neutralization of the poly(AA) andpoly(vinylamine) was changed. The various multicomponent SAP particleswere tested for an ability to absorb and retain synthetic urine, and theresults are summarized in Table 7.

                  TABLE 7                                                         ______________________________________                                        % Neutralized                                                                 Poly(vinylamine)/          AUL     AUL                                        % Neutralized Surface      (0.7 psi,                                                                             (0.7 psi,                                  Poly (AA) (by weight)                                                                       Crosslinking 1 hr)   3 hr)                                      ______________________________________                                        0/0           None         16.8    21.6                                        0/10         None         13.4    16.9                                        0/25         None         12.6    16                                         10/0          None         37.2    37.7                                       25/0          None         24.4    25.3                                       10/10         None         19.2    24.3                                       25/25         None         19.8    19.3                                       50/50         None         11.9    13.8                                       0/0           PG/H.sub.2 O.sup.25)                                                                       43.3    47.6                                        0/10         PG/H.sub.2 O 34      36.9                                        0/25         PG/H.sub.2 O 14.4    17.4                                       10/0          PG/H.sub.2 O 30.9    31.4                                       25/0          PG/H.sub.2 O 24.1    25.3                                       10/10         PG/H.sub.2 O 39.3    41.2                                       25/25         PG/H.sub.2 O 18.9    18.7                                       50/50         PG/H.sub.2 O 12.1    14.5                                       ______________________________________                                         .sup.25) Surface treatment with propylene glycol/water (80/20 ratio) as       set forth in Example 19.                                                 

In another series of tests, the ratio of acidic water-absorbing resin tobasic water-absorbing resin in the multicomponent SAP particles wasvaried. In particular, Table 8 summarizes the AUNL data and the AUL dataat different pressures for a series of multicomponent SAP particlescontaining poly(vinylamine) and poly(AA) over the range of 25% to 75% byweight. The multicomponent SAP particles used in this series of testswere prepared in accordance with the multicomponent SAP particlesprepared in Example 12, and contained 55% by weight poly(vinylamine) and45% by weight poly(acrylic acid). All multicomponent SAP particles usedin the test were surface crosslinked with 50 ppm EGDGE. Themulticomponent SAP particles were tested for an ability to absorb andretain synthetic urine.

                                      TABLE 8                                     __________________________________________________________________________    Weight                                                                        Ratio                                                                              AUL AUL AUL     AUL AUL AUL     AUL                                      Poly(vinyl                                                                         0.28                                                                              0.7 1.4     0.28                                                                              0.7 1.4     0.28                                                                              AUL AUL                              amine)/-                                                                           psi psi psi AUNL                                                                              psi psi psi AUNL                                                                              psi 0.7 psi                                                                           1.4 psi                                                                           AUNL                         Poly(AA)                                                                           (1 hr)                                                                            (1 hr)                                                                            (1 hr)                                                                            (1 hr)                                                                            (3 hr)                                                                            (3 hr)                                                                            (3 hr)                                                                            (3 hr)                                                                            (17 hr)                                                                           (17 hr)                                                                           (17 hr)                                                                           (17 hr)                      __________________________________________________________________________    25/75                                                                              41.3                                                                              36.6    53.6                                                                              41.2                                                                              36.6    54  39.1                                                                              33.3    52.3                         30/70                                                                              46.3                                                                              42.2    58.7                                                                              46.4                                                                              42.8    59.6                                                                              43.1                                                                              38.7    58.4                         35/65                                                                              43.6                                                                              38.5    54.4                                                                              44.2                                                                              39.5    54.8                                                                              42  35.8    54.3                         40/60                                                                              52.1                                                                              44.3    63.9                                                                              53.7                                                                              46.5    66.7                                                                              51.7                                                                              43.2    65.2                         45/55                                                                              50.4                                                                              46      61.i                                                                              51.4                                                                              47.4    63.2                                                                              47.3                                                                              41.9    61.9                         50/50                                                                              52.2                                                                              45  26  62.5                                                                              54.8.                                                                             47.7                                                                              29  66.7                                                                              52.8                                                                              45.4                                                                              30.9                                                                              66.4                         55/45                                                                              52.1                                                                              47.3                                                                              27.4                                                                              62.5                                                                              54.8                                                                              49.3                                                                              31.3                                                                              66.2                                                                              53.1                                                                              44.8                                                                              32.5                                                                              65.4                         60/40                                                                              52.8                                                                              47  27.8                                                                              64.6                                                                              55.2                                                                              49.6                                                                              30.9                                                                              68  52.6                                                                              44  33  67.6                         65/35                                                                              50  45.9    59.2                                                                              51.6                                                                              47.3    61.8                                                                              48.8                                                                              41      61.4                         70/30                                                                              47.5                                                                              43.1    57.4                                                                              48.3                                                                              43.8    59.4                                                                              43.5                                                                              37.2    56.7                         75/25                                                                              43.9                                                                              39.3    53.6                                                                              43.9                                                                              39.2    54.8                                                                              38.9                                                                              31.2    51.4                         __________________________________________________________________________

In another series of tests, multicomponent SAP particles containing 45%poly(AA) and 55% poly(vinylamine) by weight were prepared as set forthin Example 12. The multicomponent SAP particles were prepared byextruding the blended gels of acidic resin and basic resin using aKitchenAid mixer (as a control), or using a Brabender twin screwextruder containing both mixing and conveying elements. In some tests,additional back pressure was provided by a breaker plate and/or ascreen. The speed of the Brabender extruder was varied. Both untreatedand surface treated (i.e., PG/H₂ O 80/20) multicomponent SAP particleswere tested. The various samples were tested for an ability to absorbsynthetic urine. The results, summarized in Table 9, show that the moreintimate blending provided by the Brabender extruder improved theabsorption and retention properties of the SAP particles.

                                      TABLE 9                                     __________________________________________________________________________                                 AUL AUL     AUL AUL                                                Surface                                                                              AUNL                                                                              0.28 psi                                                                          0.7 psi                                                                           AUNL                                                                              0.28 psi                                                                          0.7 psi                          Method of Extrusion                                                                             Treatment                                                                            (1 hr)                                                                            (1 hr)                                                                            (1 hr)                                                                            (3 hr)                                                                            (3 hr)                                                                            (3 hr)                           __________________________________________________________________________    KitchenAid (control)                                                                            None   69.6                                                                              33  15.4                                                                              73.3                                                                              39.3                                                                              21.7                             Brabender-no plate 25 rpm                                                                       None   71.4                                                                              41.7                                                                              13.9                                                                              74.7                                                                              46.6                                                                              19.6                             Brabender-no plate 100 rpm                                                                      None   70.7                                                                              43.5                                                                              15.5                                                                              73.8                                                                              56.2                                                                              23.6                             Brabender-plate 25 rpm                                                                          None   72  46.7                                                                              16  74.1                                                                              55.1                                                                              22.1                             Brabender-plate 100 rpm                                                                         None   70.5                                                                              48.4                                                                              16.9                                                                              72.6                                                                              60  23.2                             Brabender-plate 150 rpm                                                                         None   69.7                                                                              50.5                                                                              29.5                                                                              72.1                                                                              59.3                                                                              35.4                             Brabender-plate 40 mesh screen 25 rpm                                                           None   70.5                                                                              54.4                                                                              16.3                                                                              73.3                                                                              59.7                                                                              23.9                             Brabender-plate 40 mesh screen 150 rpm                                                          None   68.9                                                                              57.7                                                                              33.2                                                                              69  59.9                                                                              42.1                             KitchenAid (control)                                                                            PG/H.sub.2 O 80/20                                                                   64.3                                                                              51.9                                                                              40.3                                                                              69.9                                                                              55.7                                                                              44                               Brabender-no plate 25 rpm                                                                       PG/H.sub.2 O 80/20                                                                   66.2                                                                              53.7                                                                              42  70.4                                                                              56.9                                                                              44.6                             Brabender-no plate 100 rpm                                                                      PG/H.sub.2 O 80/20                                                                   65.4                                                                              52.8                                                                              41.6                                                                              68.8                                                                              56.1                                                                              45.4                             Brabender-plate 25 rpm                                                                          PG/H.sub.2 O 80/20                                                                   66.8                                                                              53.7                                                                              42.3                                                                              70.4                                                                              56.9                                                                              45.5                             Brabender-plate 100 rpm                                                                         PG/H.sub.2 O 80/20                                                                   66  53  44  68.8                                                                              55.5                                                                              47.6                             Brabender-plate 150 rpm                                                                         PG/H.sub.2 O 80/20                                                                   65.5                                                                              52.3                                                                              44.6                                                                              67.8                                                                              54.5                                                                              47.2                             Brabender-plate 40 mesh screen 25 rpm                                                           PG/H.sub.2 O 80/20                                                                   65.2                                                                              54  45.6                                                                              68.3                                                                              56.2                                                                              49.1                             Brabender-plate 40 mesh screen 150 rpm                                                          PG/H.sub.2 O 80/20                                                                   63.5                                                                              50.7                                                                              44.2                                                                              64.9                                                                              53.1                                                                              47.1                             __________________________________________________________________________

In addition to an ability to absorb and retain relatively large amountsof a liquid, it also is important for an SAP to exhibit goodpermeability, and, therefore, rapidly absorb the liquid. Therefore, inaddition to absorbent capacity, or gel volume, useful SAP particles alsohave a high gel strength, i.e., the particles do not deform afterabsorbing a liquid. In addition, the permeability or flow conductivityof a hydrogel formed when SAP particles swell, or have already swelled,in the presence of a liquid is extremely important property forpractical use of the SAP particles. Differences in permeability or flowconductivity of the absorbent polymer can directly impact on the abilityof an absorbent article to acquire and distribute body fluids.

Many types of SAP particles exhibit gel blocking. "Gel blocking" occurswhen the SAP particles are wetted and swell, which inhibits fluidtransmission to the interior of the SAP particles and between absorbentSAP particles. Wetting of the interior of the SAP particles or theabsorbent structure as a whole, therefore, takes place via a very slowdiffusion process, possibly requiring up to 16 hours for complete fluidabsorption. In practical terms, this means that acquisition of a fluidby the SAP particles, and, accordingly, the absorbent structure, such asa diaper, can be much slower than the rate at which fluids aredischarged, especially in gush situations. Leakage from an absorbentstructure, therefore, can occur well before the SAP particles in theabsorbent structure are fully saturated, or before the fluid can diffuseor wick past the "gel blocked" particles into the remainder of theabsorbent structure. Gel blocking can be a particularly acute problem ifthe SAP particles lack adequate gel strength, and deform or spread understress after the SAP particles swell with absorbed fluid.

Accordingly, an SAP particle can have a satisfactory AUL value, but willhave inadequate permeability or flow conductivity to be useful at highconcentrations in absorbent structures. In order to have a high AULvalue, it is only necessary that the hydrogel formed from the SAPparticles has a minimal permeability such that, under a confiningpressure of 0.3 psi, gel blocking does not occur to any significantdegree. The degree of permeability needed to simply avoid gel blockingis much less than the permeability needed to provide good fluidtransport properties. Accordingly, SAPs that avoid gel blocking and havea satisfactory AUL value can still be greatly deficient in these otherfluid handling properties.

Accordingly, an important characteristic of the multicomponent SAPparticles of the present invention is permeability when swollen with aliquid to form a hydrogel zone or layer, as defined by the Saline FlowConductivity (SFC) value of the SAP particles. SFC measures the abilityof an SAP to transport saline fluids, such as the ability of thehydrogel layer formed from the swollen SAP to transport body fluids. Amaterial having relatively high SFC value is an air-laid web of woodpulpfibers. Typically, an air-laid web of pulp fibers (e.g., having adensity of 0.15 g/cc) exhibits an SFC value of about 200×10⁻⁷ cm³ sec/g.In contrast, typical hydrogel-forming SAPs exhibit SFC values of 1×10⁻⁷cm³ sec/g or less. When an SAP is present at high concentrations in anabsorbent structure, and then swells to form a hydrogel under usagepressures, the boundaries of the hydrogel come into contact, andinterstitial voids in this high SAP concentration region becomegenerally bounded by hydrogel. When this occurs, the permeability orsaline flow conductivity properties in this region is generallyindicative of the permeability or saline flow conductivity properties ofa hydrogel zone formed from the SAP alone. Increasing the permeabilityof these swollen high concentration regions to levels that approach oreven exceed conventional acquisition/distribution materials, such aswood pulp fluff, can provide superior fluid handling properties for theabsorbent structure, thus decreasing incidents of leakage, especially athigh fluid loadings.

Accordingly, it would be highly desirable to provide SAP particleshaving an SFC value that approaches or exceeds the SFC value of anair-laid web of wood pulp fibers. This is particularly true if high,localized concentrations of SAP particles are to be effectively used inan absorbent structure. High SFC values also indicate an ability of theresultant hydrogel to absorb and retain body fluids under normal usageconditions.

The SFC value of the present multicomponent SAP particles aresubstantially improved over the SFC value for a standard poly(AA) SAP,as illustrated in the data summarized in Table 10. A method fordetermining the SFC value of SAP particles is set forth in Goldman etal. U.S. Pat. No. 5,599,335, incorporated herein by reference.

                                      TABLE 10                                    __________________________________________________________________________        Sample 1                                                                            Sample 2                                                                (Control) .sup.26)                                                                  (Comparative) .sup.27)                                                                Sample 3 .sup.28)                                                                   Sample 4 .sup.29)                                                                   Sample 5 .sup.30)                                                                   Sample 6 .sup.31)                                                                   Sample 7 .sup.32                    Time                                                                              AUL   AUL     AUL   AUL   AUL   AUL   AUL                                 (min)                                                                             0.7 psi                                                                             0.7 psi 0.7 psi                                                                             0.7 psi                                                                             0.7 psi                                                                             0.7 psi                                                                             0.7 psi                             __________________________________________________________________________     0  0     0       0     0     0     0     0                                    5  25.3  14.8    26    26.3  17.8  19.3  13.6                                10  30.7  20.9    33.2  34.5  23.4  20.4  16.2                                15  32.1  25.1    37.9  38.8  26.3  21    17.4                                30  33.8  31.2    43.3  44.1  29.9  20.8  17.6                                45  34.2  34.3    45.8  45.6  31.8  21.6  19.3                                60  34.5  36.4    47.6  46.2  32.4  21.7  20.1                                120 35.2  40      49.1  47.6  33.6  22.3  20.5                                180 35.2  42.3    49.7  48    35.6  22.8  21.7                                SFC .sup.33)                                                                      15    115     368   685   707   534   930                                 __________________________________________________________________________     .sup.26) Standard, commercial SAP, i.e., neutralized poly(AA), 75% DN,        available as A2300, from Chemdal, Corp., Palatine, IL;                        .sup.27) Comparative sample containing a dry blend of 55% by weight           unneutralized poly(vinylamine) particles and 45% by weight unneutralized      poly(AA) particles;                                                           .sup.28) Multicomponent SAP particles of the present invention, containin     55% unneutralized poly(vinylamine) and 55% poly(AA), prepared in a            KitchenAid mixer in accordance with Example 12;                               .sup.29) Multicomponent SAP particles of the present invention, containin     55% unneutralized poly(vinylamine) and 45% poly(AA), prepared in              accordance with Example 12;                                                   .sup.30) Multicomponent SAP particles of the present invention, containin     55% unneutralized poly(vinylamine) and 45% poly(AA), prepared in              accordance with Example 12;                                                   .sup.31) Multicomponent SAP particles of the present invention, containin     55% unneutralized poly(vinylamine) and 45% poly(AA), prepared in              accordance with Example 20;                                                   .sup.32) Multicomponent SAP particles of the present invention, containin     55% unneutralized poly(vinylamine) and 45% poly(AA), prepared in              accordance with Example 21; and                                               .sup.33) in ×10.sup.-7 cm.sup.3 sec/g.                             

The data summarized in Table 10 shows a substantial improvement in AULat 0.7 psi and SFC for multicomponent particles of the present inventionin comparison to a control SAP and a comparative dry blend of SAPparticles. Accordingly, a present multicomponent SAP particle has an SFCvalue of at least about 150×10⁻⁷ cm³ sec/g, and preferably at leastabout 250×10⁻⁷ cm³ sec/g. To achieve the full advantage of the presentinvention, the SFC value is at least about 350×10⁻⁷ cm³ sec/g, and canrange to greater than 1000×10⁻⁷ cm³ sec/g.

The present multicomponent SAP particles also exhibit excellentdiffusion of a liquid through and between the particles. FIG. 8 containsplots of Performance Under Pressure (PUP) capacity at 0.7 psi over timefor a dry blend of 55% unneutralized poly(vinylamine) and 45%unneutralized poly(AA), for a standard commercial poly(AA) SAP, and fora present multicomponent SAP. The PUP capacity test is similar to theAUL test, but the SAP particles are allowed to absorb a fluid on demand.The PUP test is designed to illustrate absorption kinetics of an SAPparticle.

In contrast, the plots of FIG. 8 illustrate that the presentmulticomponent SAP particles (i.e., 55/45 weight ratio unneutralizedpoly(vinylamine)/poly(AA) particles prepared using a Brabender extruderin accordance with Example 12 and annealed for 1 hour at 125° C.)essentially attain their absorptive capacity after 1 hour, and haveattained their absorptive capacity after 3 hours. The plots show thatafter 3 hours, the PUP capacity of the dry blend has not been attained.The present multicomponent SAP particles, therefore, demonstrate afaster absorption of liquids, and a better diffusion rate of liquidsinto and through the particles, in addition to an ability to absorb andretain a greater amount of liquids than prior or other SAP products.

FIG. 8 also shows that a standard poly(AA) attains an absorptivecapacity quickly, but does not absorb and retain as much of theelectrolyte-containing liquid. Overall, FIG. 8 shows that the presentmulticomponent SAPs exhibit both a) improved absorption and retention,and b) improved permeability and absorption kinetics. Such results areboth new and unexpected in the art.

FIG. 9 contains similar plots again showing improved absorption,retention, permeability, and absorption kinetics for a multicomponentSAP particle identical to those used in FIG. 8, except the particlestested in FIG. 9 were surface coated with 80/20 PG/H₂ O and heated at125° C. for 1 hour.

FIGS. 10 and 11 illustrate the improved initial performance underpressure (PUP) capacity rate for multicomponent SAP particles of thepresent invention. FIG. 10 shows the comparative initial PUP capacityrate for absorbency vs. (time)^(1/2) for 16 hours between multicomponentSAP particles containing a 55/45 weight ratio of poly(vinylamine) andpoly(acrylic acid) surface crosslinked with 80/20 PG/H₂ O, a dry blendof poly(vinylamime) and poly(acrylic acid), and a standard 75%neutralized poly(AA) SAP. The plots in FIG. 10 provide a bettermeasurement of the initial slope of the plots, and, therefore, providesa more meaningful comparison of initial PUP capacity rate.

The plots in FIG. 10 show a substantially improved initial PUP capacityrate for the multicomponent SAP particles prepared using a KitchenAidmixer (93.2 g/g/hr^(1/2)) compared to a dry blend of SAP particles (40.7g/g/hr^(1/2)) and to a standard poly(AA) (40.1 g/g/hr^(1/2)). FIG. 11shows similar results for multicomponent SAP particles prepared in aBrabender extrusion apparatus and annealed for 1 hour at 125° C., i.e.,initial PUP capacity of 104.2 g/g/hr^(1/2).

A multicomponent SAP practice of the present invention, therefore, hasan initial PUP is capacity rate of at least 50 g/g/hr^(1/2), andpreferably at least 70 g/g/hr^(1/2). To achieve the full advantage ofthe present invention, the multicomponent SAP particle has an initialPUP capacity rate of greater than 90 g/g/hr^(1/2), and preferablygreater than 100 g/g/hr^(1/2).

In another test, the free swell rate (FSR) of a present multicomponentSAP particle was com- pared to the FSR of a standard poly(AA) SAP and55/45 weight ratio of a poly(vinylamine)/poly(acrylic acid) dry particleblend. The FSR test is well known to persons skilled in the art.

The present multicomponent SAP particles had an FSR (in g/g/sec) of 0.49and 0.48, for 55/45 weight ratio multicomponent SAP particles made in aKitchenAid mixer and a Brabender extruder, respectively. In comparison,a dry blend had an FSR of 0.10 and a standard neutralized poly(AA) hadan FSR of 0.32. Multicomponent SAP particles of the present invention,therefore, have an FSR of greater than 0.35, preferably greater than0.40, and most preferably greater than 0.45. These data further show theimproved ability of the present SAP particles to absorb and retainlarger amounts of an electrolyte-containing liquid quickly.

Many modifications and variations of the invention as hereinbefore setforth can be made without departing from the spirit and scope thereofand, therefore, only such limitations should be imposed as are indicatedby the appended claims.

What is claimed is:
 1. A multicomponent superabsorbent particlecomprising at least one microdomain of at least one basicwater-absorbing resin dispersed in a continuous phase of at least oneacidic water-absorbing resin.
 2. The particle of claim 1 wherein thebasic resin comprises a strong basic resin, and the acidic resincomprises a strong acidic resin, a weak acidic resin, or a mixturethereof.
 3. The particle of claim 1 wherein the basic resin comprises aweak basic resin, and the acidic resin comprises a strong acidic resin,a weak acidic resin, or a mixture thereof.
 4. The particle of claim 1having a weight ratio of acidic resin to basic resin of about 90:10 toabout 10:90.
 5. The particle of claim 1 containing about 50% to 100%, byweight, of basic resin plus acidic resin.
 6. The particle of claim 1wherein the particle is about 10 to about 10,000 microns in diameter. 7.The particle of claim 1 wherein the basic resin is annealed at atemperature of about 65° C. to about 150° C. for about 20 minutes toabout 16 hours.
 8. The particle of claim 1 wherein the basic resin issurface crosslinked with up to about 1% by weight of the particle of asurface crosslinking agent.
 9. The particle of claim 8 wherein thesurface crosslinking agent is selected from the group consisting of(a) adihalide or a disulfonate ester having the formula

    Y--(CH.sub.2).sub.p --Y,

wherein p is an integer 2 to 12 and Y, independently, is halo, tosylate,mesylate, an alkyl sulfonate ester, or an aryl sulfonate ester; (b) amultifunctional aziridine; (c) a multifunctional aldehyde, and acetalsand bisulfites thereof; (d) a halohydrin; (e) a multifunctional epoxycompound; (f) a multifunctional carboxylic acid containing 2 to 12carbon atoms, and methyl and ethyl esters, acid chlorides, andanhydrides derived therefrom; (g) an organic titanate; (h) a melamineresin; (i) a hydroxymethyl urea; (j) a multifunctional isocyanate; and(k) mixtures thereof.
 10. The particle of claim 9 wherein the surfacecrosslinking agent is selected from the group consisting of apolyhydroxy compound, a metal salt, a quaternary ammonium compound, amultifunctional epoxy compound, an alkylene carbonate, a polyaziridine,a haloepoxy, a polyamine, a polyisocyanate, and mixtures thereof. 11.The particle of claim 1 wherein the particle is surface crosslinked withup to about 10,000 ppm of a surface crosslinking agent.
 12. The particleof claim 1 wherein the particle is annealed at a temperature of about65° C. to about 150° C. for about 20 minutes to about 16 hours.
 13. Theparticle of claim 1 wherein the basic resin has about 75% to 100% basicmoieties present in a free base form.
 14. The particle of claim 1wherein the basic resin is lightly crosslinked.
 15. The particle ofclaim 1 wherein at least 6% of the monomer units comprising the basicresin are basic monomer units.
 16. The particle of claim 1 wherein thebasic resin is selected from the group consisting of a poly(vinylamine),a poly(dialkylaminoalkyl (meth)acrylamide), a polymer prepared from theester analog of an N-(dialkyamino(meth)acrylamide), a polyethylenimine,a poly(vinylguanidine) a poly(allylguanidine), a poly(allylamine), apoly(dimethyldialkylammonium hydroxide), a guanidine-modifiedpolystyrene, a quaternized polystyrene, a quaternizedpoly(meth)acrylamide or ester analog thereof, poly(vinylalcohol-co-vinylamine), and mixtures thereof.
 17. The particle of claim1 wherein the acidic resin contains a plurality of carboxylic acid,sulfonic acid, sulfuric acid, phosphonic acid, or phosphoric acidgroups, or a mixture thereof.
 18. The particle of claim 1 wherein theacidic resin has about 75% to 100% acid moieties present in the freeacid form.
 19. The particle of claim 1 wherein at least 10% of themonomer units comprising the acidic resin are acidic monomer units. 20.The particle of claim 1 wherein the acidic resin is lightly crosslinked.21. The particle of claim 1 wherein the acidic resin is selected fromthe group consisting of polyacrylic acid, a hydrolyzedstarch-acrylonitrile graft copolymer, a starch-acrylic acid graftcopolymer, a saponified vinyl acetate-acrylic ester copolymer, ahydrolyzed acrylonitrile polymer, a hydrolyzed acrylamide copolymer, anethylene-maleic anhydride copolymer, an isobutylene-maleic anhydridecopolymer, a poly(vinylphosphonic acid), a poly(vinylsulfonic acid), apoly(vinylphosphoric acid), a poly(vinyl-sulfuric acid), a sulfonatedpolystyrene, a poly(aspartic acid), a poly(lactic acid), and mixturesthereof.
 22. The particle of claim 1 wherein the basic resin comprises apoly(vinylamine), a poly(dialkylaminoalkyl (meth)acrylamide), apoly(vinylguanidine), a polyethylenimine, or a mixture thereof, and theacidic resin comprises poly(acrylic acid).
 23. The particle of claim 22wherein the poly(dialkylaminoalkyl (meth)acrylamide) comprisespoly(dimethylaminoethyl acrylamide), poly(dimethylaminopropylmethacrylamide), or a mixture thereof.
 24. The particle of claim 22wherein the poly(acrylic acid) resin further contains strong acidmoieties.
 25. An article comprising a multicomponent superabsorbentparticle of claim
 1. 26. The article of claim 25, wherein the article isa diaper or a catamenial device.
 27. A method of absorbing an aqueousmedium comprising contacting the medium with a plurality of particles ofclaim
 1. 28. A method of claim 27 wherein the aqueous medium containselectrolytes.
 29. A method of claim 28 wherein theelectrolyte-containing aqueous medium is selected from the groupconsisting of urine, saline, menses, and blood.
 30. A multicomponentsuperabsorbent particle comprising at least one microdomain of at leastone acidic water-absorbing resin dispersed in a continuous phase of atleast one basic water-absorbing resin.
 31. A method of absorbing anaqueous medium comprising contacting the medium with a particle of claim30.
 32. A multicomponent superabsorbent particle comprising at least onemicrodomain of at least one basic water-absorbing resin and at least onemicrodomain of at least one acidic water-absorbing resin dispersed in acontinuous phase of a matrix resin.
 33. The particle of claim 32comprising 25% to 50%, by weight, of a matrix resin.
 34. The particle ofclaim 32 wherein the matrix resin comprises a hydrophilic resin.
 35. Amethod of absorbing an aqueous medium comprising contacting the mediumwith a particle of claim
 32. 36. A multicomponent superabsorbentparticle comprising at least one microdomain of at least one basicwater-absorbing resin in contact with at least one microdomain of atleast one acidic water-absorbing resin.
 37. The particle of claim 36further comprising at least one microdomain of a matrix resin in anamount of 0% to 50% by weight of the particle.
 38. The particle of claim36 consisting essentially of microdomains of the acidic resin and thebasic resin.
 39. A method of absorbing an aqueous medium comprisingcontacting the medium with a particle of claim
 36. 40. A multicomponentsuperabsorbent particle comprising at least one microdomain of a firstwater-absorbing resin in contact with at least one microdomain of asecond water-absorbing resin.
 41. The particle of claim 40 in the formof a bead, a granule, a flake, an interpenetrating polymer network, afiber, an agglomerated particle, a laminate, a powder, a foam, or asheet.
 42. The particle of claim 40 having an absorption under load at0.7 psi of at least about 10 grams of 0.9% saline per gram of particles,after one hour, and at least about 10 grams of 0.9% saline per gram ofparticles after three hours.
 43. The particle of claim 40 having asaline flow conductivity value of at least 150×10⁻⁷ cm³ sec/g.
 44. Theparticle of claim 40 having an initial performance under pressurecapacity rate of greater than 50 g/g/hr^(1/2).
 45. The particle of claim40 having a free swell rate greater than 0.35 g/g/sec.
 46. The particleof claim 40 wherein the first resin comprises a basic water-absorbingresin, and the second resin comprises an acidic water-absorbing resin.47. The particle of claim 40 wherein the first resin comprises an acidicwater-absorbing resin, and the second resin comprises a mixture of amatrix resin and a basic water-absorbing resin.
 48. A multicomponentsuperabsorbent particle comprising at least one microdomain of an acidicwater-absorbing resin in close proximity to at least one microdomain ofa basic water-absorbing resin in a single particle.